Dominant glacial landforms of the lower Great Lakes region exhibit different soil phosphorus chemistry and potential risk for phosphorus loss

Phosphorus (P) losses from agricultural soils are a growing economic and water-quality concern in the Lake Erie watershed. While recent studies have explored edge-of-field and watershed P losses related to land-use and agricultural management, the potential for soils developed from contrasting parent materials to retain or release P to runoff has not been examined. A field-based study comparing eight agricultural fields in contrasting glacial landscapes (hummocky coarse-textured till-plain, lacustrine and fine-textured till-plain) showed distinct physical and geochemical soil properties influencing inorganic P (P_i) partitioning throughout the soil profile between the two regions. Fields located on the coarse-textured till-plain in mid-western Ontario, Canada had alkaline calcareous soils with the highest Total-P_i concentrations and the majority of soil P_i stored in an acid-soluble pool (up to 91%). In contrast, loosely to moderately soluble P_i concentrations were higher in soils of the lacustrine and fine-textured till-plain in southwestern Ontario, northeast Indiana and northwestern Ohio, US. Overall, soils on the lacustrine and fine-textured till-plain had a greater shrink swell-capacity, likely creating preferential flow to minimize P_i interaction with the more acidic, lower carbonate and lower sorption capacity soils. These differences in soil P_i retention and transport pathways demonstrate that in addition to management, the natural landscape may exert a significant control on how P_i is mobilized throughout the Lake Erie watershed. Further, results indicate that careful consideration of region-specific hydrology and soil biogeochemistry may be required when designing appropriate management strategies to minimize P_i losses across the lower Great Lakes region.     

Periphytic algal biomass as a bioindicator of phosphorus concentrations in agricultural headwater streams of southern Ontario

Algal blooms in Lake Erie have worsened in recent decades and are driven by diffuse export of phosphorus (P) from a large stream network that drains predominately agricultural land. Given the diffuse nature of nonpoint source pollution, best management practices (BMPs) must target areas where P levels are high. This requires long-term watershed-wide monitoring programs that do not currently exist in many jurisdictions. Instead of conventional nutrient analyses that can be costly and time-consuming, we propose the use of periphyton biomass as a bioindicator of trophic status in low-order streams, where agricultural runoff first enters watercourses. We carried out 2-week in-stream bioassays to measure periphytic algal biomass (CHL_peri) in 19 low-order streams in southern Ontario across an agricultural gradient (8 % to 89 %). CHL_peri was significantly related to total P (TP) concentration (r² = 0.46; p = 0.0015) but was not significantly related to soluble reactive P (SRP). A relationship between TP and turbidity (r² = 0.52; p = 0.0007) is consistent with previous observations of increasing SRP uptake in streams draining agriculturally-dominated landscapes. Stream temperature (°C) was correlated with the proportion of agricultural land (R = 0.55; p = 0.019) and may reflect the warming effects of the sun in unshaded agricultural streams. This method involving substrate rods (Peristix) is cost-effective, requires very little training, and yielded data that were significantly related to TP concentrations in agricultural streams. We recommend that environmental agencies and landowners use this bioassay to identify areas for implementing BMPs to reduce P export from the Lake Erie watershed.     

Morphological evidence of discrete stocks of yellow perch in Lake Erie

Identification and management of unique stocks of exploited fish species are high-priority management goals in the Laurentian Great Lakes. We analyzed whole-body morphometrics of 1430 yellow perch Perca flavescens captured during 2007–2009 from seven known spawning areas in Lake Erie to determine if morphometrics vary among sites and management units to assist in identification of spawning stocks of this heavily exploited species. Truss-based morphometrics (n = 21 measurements) were analyzed using principal component analysis followed by ANOVA of the first three principal components to determine whether yellow perch from the several sampling sites varied morphometrically. Duncan's multiple range test was used to determine which sites differed from one another to test whether morphometrics varied at scales finer than management unit. Morphometrics varied significantly among sites and annually, but differences among sites were much greater. Sites within the same management unit typically differed significantly from one another, indicating morphometric variation at a scale finer than management unit. These results are largely congruent with recently-published studies on genetic variation of yellow perch from many of the same sampling sites. Thus, our results provide additional evidence that there are discrete stocks of yellow perch in Lake Erie and that management units likely comprise multiple stocks.     

Demonstrating the relationship between soil phosphorus measures and phosphorus solubility: Implications for Ohio phosphorus risk assessment tools

Approximately 80% of the land area draining into the western Lake Erie Basin is in Ohio, much of which is agricultural. Therefore, the potential for agricultural phosphorus (P) loading from Ohio is a concern for the water quality of western basin rivers, embayments and open water. This work demonstrates soil P relationships across Ohio soils and its implications for potential revisions of Ohio P risk assessment tools. The objectives were, using a selection of soils representative of soils across Ohio, (i) to determine if soil survey classification (series) could be an indicator of hydrous oxide content and, (ii) to determine if agronomic soil test P (STP) Mehlich 3 (M3-P), Bray P, or alternative measures of soil P saturation (Psat) were comparable to oxalate Psat for predicting P solubility, and therefore, useful for Ohio P risk assessment tools. Results showed no significant difference (P > 0.01) in soil hydrous oxide content when grouped by soil series. However, significant (P < 0.01) inflection points, reflecting a rapid increase in P solubility, were identified for oxalate P saturation (11.8%), M3-P saturation (12.4%), M3-P extractable P (181 mg/kg), and Bray-P extractable P (122 mg/kg). This suggests a separate pre- and post-inflection point consideration of STP may be appropriate for revised Ohio P risk assessment tools to better reflect increased post-inflection offsite P transport risk and thereby be sufficiently protective of water quality. Identifying fields with high offsite P transport risk is critical to implementing management decisions to reduce P transport risk to receiving waters including Lake Erie.     

Genome-wide genetic diversity may help identify fine-scale genetic structure among lake whitefish spawning groups in Lake Erie

In Lake Erie, lake whitefish Coregonus clupeaformis supported lucrative fisheries before populations were decimated by overfishing and water quality degradation. In recent years, there has been a renewed interest in lake whitefish and management of the fishery they support. Lake whitefish spawn on several reefs throughout Lake Erie, but the relative recruitment dynamics and contributions of spawning groups to the fishery are not well understood. Modern high-throughput sequencing approaches offer new opportunities to census population diversity and to identify subtle differences among closely related populations. We used high-throughput sequencing data to evaluate the genetic structure and diversity of lake whitefish collected opportunistically across broad spatial scales in Lake Erie. Using RAD-capture (Rapture), we sequenced and genotyped individuals (N = 88) from the west, central, and east basin of Lake Erie at 120,268 single nucleotide polymorphisms (SNPs). Lake whitefish from Niagara and Crib Reefs (west basin) diverged from the three collections. Interestingly, these were the only lake whitefish collected during the act of spawning (late November), and all other fish were collected pre-spawn (August-early November). These results suggest that some lake whitefish spawning reefs may be reproductively isolated, though definition of these groups into stocks will require more intentional sampling during the act of spawning.     

Historical changes and current status of crayfish diversity and distribution in the Laurentian Great Lakes

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although O. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. O. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions.     

A Bayesian hierarchical spatially explicit modelling framework to examine phosphorus export between contrasting flow regimes

We examine the ability of a SPARROW-based model (SPAtially Referenced Regression On Watershed attributes) to assess regional P export coefficients that can assist with evaluation of nutrient mitigation projects and support adaptive watershed management. Limitations in number of tributary monitoring stations were overcome by assembling multi-agency water quality data from provincial, municipal, citizen science, and academic programs. We introduced a Bayesian hierarchical framework designed to guide parameter estimation from tributary nutrient loading in southern Georgian Bay drainage basin during contrasting flow regimes, such as dry and wet years. Agriculture was identified as a major non-point P source representing between 30 and 48% of delivered P loading. Our source apportionment predicted TP loss rates from croplands that exceeded those from forested areas by 320% during dry years and by 360% during wet years, while low intensity agricultural areas (hay and pasture) exceeded P export from forests by a mere 20% and 30%, respectively. Our study identified urban runoff as another significant non-point nutrient source displaying the highest variability between dry and wet years. In particular, owing to the extensive urbanization in the Lake Simcoe watershed, urban runoff contributed nearly half of delivered P loading from tributaries into the lake. The nutrient loading management plan for Lake Simcoe calls for a reduction in P loading by ～40% from a long-term average of 72 t P y^?1 in 2002–2007 to 44 t P y^?1 by 2045. Our analysis emphasizes the importance of mitigating urban non-point sources together with efforts to control agricultural runoff.     

Estimation of phosphorus loads from septic systems to tributaries in the Canadian Lake Erie Basin

The contribution of septic systems to watershed nutrient loads is poorly quantified although they are often cited as potentially important nutrient sources. The study used a geospatial model to estimate P loads from septic systems to the tributaries of the Canadian Lake Erie Basin to inform Lake Erie nutrient management initiatives. There is currently no inventory of septic systems in the Lake Erie Basin (e.g., numbers and locations of septic systems). Therefore a geospatial model was developed to automatically locate individual septic systems and to use these locations to estimate P load contributions to tributaries. The model was first tested on three subwatersheds in the Canadian Lake Erie Basin before being applied across the Basin. Present-day basin-wide P load estimates reveal that: (i) only a fraction of septic effluent is currently reaching the tributaries due to slow transport and other delays, as well as (ii) P attenuation in the subsurface, range from 23 ± 11 to 68 ± 32 MT/yr. Based on these estimates, septic systems may currently contribute 1.7 ± 0.8–5 ± 2.3% of the P loads to Lake Erie from Canada. However, maximum P load estimates and transient model results show that the contribution of septic systems to P loads will increase over time as slow moving septic-derived groundwater P plumes reach tributaries if aging septic systems are not maintained. This study provides widely applicable new knowledge and methodology; as well as specific findings needed to inform nutrient and septic system management in the Lake Erie Basin.     

Identifying sources and year classes contributing to invasive grass carp in the Laurentian Great Lakes

Relative contributions of aquaculture-origin and naturally-reproduced grass carp (Ctenopharyngodon idella) in the Laurentian Great Lakes have been unknown. We assessed occurrence and distribution of aquaculture-origin and wild grass carp in the Great Lakes using ploidy and otolith stable oxygen isotope (δ¹⁸O) data. We inferred natal river and dispersal from natal location for wild grass carp using otolith microchemistry and estimated ages of wild and aquaculture-origin fish to infer years in which natural reproduction and introductions occurred. Otolith δ¹⁸O indicated that the Great Lakes contain a mixture of wild grass carp and both diploid and triploid, aquaculture-origin grass carp. Eighty-eight percent of wild fish (n = 49 of 56) were caught in the Lake Erie basin. Otolith microchemistry indicated that most wild grass carp likely originated in the Sandusky or Maumee rivers where spawning has previously been confirmed, but results suggested recruitment from at least one other Great Lakes tributary may have occurred. Three fish showed evidence of movement between their inferred natal river in western Lake Erie and capture locations in other lakes in the Great Lakes basin. Age estimates indicated that multiple year classes of wild grass carp are present in the Lake Erie basin, recruitment to adulthood has occurred, and introductions of aquaculture-origin fish have happened over multiple years. Knowledge of sources contributing to grass carp in the Great Lakes basin will be useful for informing efforts to prevent further introductions and spread and to develop strategies to contain and control natural recruitment.     

A Bayesian network model for bluff retreat on the southern Lake Erie coast,United States

Coastal bluffs on the 73 km Pennsylvania mainland coast of Lake Erie consist of unconsolidated glacial through paleo-lacustrine Quaternary strata overlying Devonian shale bedrock. Erosion is a significant environmental hazard on this coast where the long-term average annual retreat rate at the bluff crest is ∼ 0.15 m/yr. As the primary geomorphic feature used to track land loss on high-relief coasts, understanding the processes that drive bluff-crest retreat and concomitant sediment and infrastructure losses remains a challenge in coastal-hazard management. This paper shows that bluff retreat on the Lake Erie coast of Pennsylvania can be successfully modeled using multivariate statistics that may have application to bluff settings across the Great Lakes basin and globally. A Bayesian Network (BN) model is developed using long-term historical data (1938–2007 training datasets) and validated against subsequent crest retreat mapped from recent lidar data. Seven field sites were sampled for environmental data that collectively covered ∼ 30 % of the 33.5 km length of the western Erie County littoral cell (WECLC). A BN with eight inputs correctly predicted bluff retreat rates for 95.4 % of transects and had a mean posterior predictive probability of 84.1 %. Scenarios show that greater crest-retreat rates were more likely to be associated with greater wave impact hours, less-resistant stratigraphy, narrower beaches, lower and steeper bluffs, a more energetic run-up regime, and a lower or absent bedrock-toe ledge. These diagnostic attributes should be useful across the WECLC to help identify, with finer spatial resolution, sectors with higher probabilities of having or developing significant erosion problems.     

Phosphorus export from artificially drained fields across the Eastern Corn Belt

Field observations that quantify agricultural phosphorus (P) losses are critical for the development of P reduction strategies across the Eastern Corn Belt region of North America. Within this region, surface water bodies including Lake Erie are sensitive to non-point P loadings. It is therefore imperative to quantify the impact of agricultural crop production on surface and subsurface water quality. This study characterized discharge, P concentrations, and P loads in surface runoff and subsurface drainage from 38 edge-of-field research sites in Ohio. Over the four-year study period, 31 ± 16% (mean ± one standard deviation) of annual precipitation became subsurface discharge while 7 ± 8% became surface discharge. Subsurface discharge accounted for 81 ± 23% of annual discharge, 71 ± 26% of annual dissolved reactive phosphorus (DRP) load, and 69 ± 27% of annual total phosphorus (TP) load. A P balance was also developed using management and loading data from the study sites. Under prevailing management practices, P removal (i.e., surface losses, subsurface losses, crop uptake) was greater than P input (i.e., atmospheric deposition, fertilizer application) on 60% of fields. Even so, further reduction of edge-of-field P losses will likely be necessary to meet watershed-scale P load recommendations. Findings suggest that balancing P inputs with crop uptake may not be sufficient to reduce edge-of-field losses due to a combination of legacy P and high-intensity rainfall events. Implementation of management practices targeting P-source will be needed in conjunction with practices at the edge-of-field targeting P-transport in order to meet recommended P loading targets in the Eastern Corn Belt region.     

Patterns in spatial use of land-locked Atlantic salmon (Salmo salar) in a large lake

Understanding the spatial use of reintroduced fish is useful for fisheries management and evaluating restoration success. Atlantic salmon (Salmo salar) were reintroduced into Lake Ontario in the 1990s; however, the movement ecology of these land-locked fish is unknown. Using acoustic telemetry and Floy tag mark-recaptures, we examined seasonal home range and space use of Atlantic salmon in Lake Ontario. Hatchery-raised adult Atlantic salmon were tagged with acoustic transmitters (n = 14; 8 with depth sensors) or Floy tags (n = 1915) and released. Both acoustic telemetry and Floy tag recaptures (n = 90) indicated cross lake movements, and home ranges encompassed nearly the entire lake in summer but was smaller in winter. Movements were nearshore (<2 km from shore) from spring to summer at ～20 m bathymetric depths, with movements closer to shore in the fall, and further offshore (～5.5 km from shore and 45 m bathymetric depths) in winter. Depth use was relatively shallow (<4 m) with occasional deeper dives (max = 28.5 m), and small diel vertical movements (1–5 m), moving deeper during daytime, consistent with ocean movements of Atlantic salmon. There appears to be spatial segregation among Atlantic salmon and other Lake Ontario salmonids, however, overlap likely occurs in nearshore waters during the spring. Wide-ranging movements of Atlantic salmon in binational (Canada/USA) waters reflects the importance of government agencies collaborating to ensure sustainable fisheries and the coordination of species restoration activities. This is the first study to provide detailed spatial use of Lake Ontario Atlantic salmon to assist in the management of this reintroduced species.     

The impact of agricultural best management practices on downstream systems: Soil loss and nutrient chemistry and flux to Conesus Lake,New York,USA

Six small, predominantly agricultural (> 70%) watersheds in the Conesus Lake catchment of New York State, USA, were selected to test the impact of Best Management Practices (BMPs) on mitigation of nonpoint nutrient sources and soil loss from farms to downstream aquatic systems. Over a 5-year period, intensive stream water monitoring and analysis of covariance provided estimates of marginal means of concentration and loading for each year weighted by covariate discharge. Significant reductions in total phosphorus, soluble reactive phosphorus, nitrate, total Kjeldahl nitrogen, and total suspended solids concentration and flux occurred by the second year and third year of implementation. At Graywood Gully, where Whole Farm Planning was practiced and a myriad of structural and cultural BMPs were introduced, we observed the greatest percent reduction (average = 55.8%) and the largest number of significant reductions in analytes (4 out of 5). Both structural and cultural BMPs were observed to have profound effects on nutrient and soil losses. Where fields were left fallow or planted in a vegetative type crop, reductions, especially in nitrate, were observed. Where structural implementation occurred, reductions in total fractions were particularly evident. Where both were applied, major reductions in nutrients and soil occurred. After 5 years of management, nonevent and event concentrations of total suspended solids in streams draining agricultural watersheds were not significantly different from those in a relatively “pristine/reference” watershed. This was not the case for nutrients.     

Agricultural conservation practices could help offset climate change impacts on cyanobacterial harmful algal blooms in Lake Erie

Harmful algal blooms (HABs) are a recurring problem in many temperate large lake and coastal marine ecosystems, caused mainly by anthropogenic eutrophication. Implementation of agricultural conservation practices (ACPs) offers a means to reduce non-point source nutrient runoff and mitigate HABs. However, the effectiveness of ACPs in a changing climate remains uncertain. We used an integrated biophysical modeling approach to predict how Lake Erie cyanobacterial HAB severity (bloom biomass) may change under several climate and ACP implementation scenarios, using western Lake Erie and its largely agricultural watershed as our study system. An ensemble of general circulation model projections was used to drive spatially explicit land use and hydrology models of the Maumee River watershed, the output of which informed a predictive model of Lake Erie HAB severity. Results show that, in the absence of changes in ACPs, the frequency of severe HABs is projected to increase during coming decades, owing to increased inputs of nutrients from the watershed. These anticipated increases are due to increased total precipitation and more frequent higher-magnitude rainfall events. While further implementation of ACPs appears capable of reducing severe HAB events, widespread implementation would be necessary to reduce HAB severity below current management targets. This study highlights how continued climate change will only exacerbate the need for land management practices that can reduce nutrient runoff in agriculturally dominated ecosystems, such as Lake Erie. It also shows how interdisciplinary, biophysical modeling approaches can help identify strategies to mitigate HABs in the face of anthropogenic stressors.     

Evaluating sediments as an ecosystem service in western Lake Erie via quantification of nutrient cycling pathways and selected gene abundances

Lake Erie experiences annual summer cyanobacterial harmful algal blooms (HABs), comprised mostly of non-nitrogen-fixing Microcystis, due to excess nitrogen (N) and phosphorus (P) inputs (eutrophication). Lake Erie's watershed is mostly agricultural, and fertilizers, manure, and drainage practices contribute to high nutrient loads. This study aimed to clarify the role of western Lake Erie sediments in either exacerbating or mitigating conditions that fuel HABs via recycling and/or removal, respectively, of excess N and reactive P. Sediment-water interface N and orthophosphate (ortho-P) dynamics and functional gene analyses of key N transformations were evaluated during a dry, low HAB year (2016) and a wet, high HAB year (2017). On average, western basin sediments were a net N sink and thus perform a valuable ecosystem service via N removal. However, sediments were a source of ortho-P and chemically reduced N. Western basin sediments can theoretically remove 29% of average annual watershed total N loading. Denitrification rates were lower during the high (2017) versus low bloom year (2016), suggesting that high external N loading and large HABs inhibit the capacity of sediments to perform that ecosystem service. Despite being a net N sink on average, western basin sediments released ammonium and urea, chemically reduced N forms that are energetically conducive to non-N-fixing, toxin-producing cyanobacterial HABs, especially during the critical period of low external loading and high biomass. These results support other recent work highlighting the urgent need to include N cycling and internal load dynamics in ecosystem models and mitigation efforts for eutrophic systems.     

Linking multi-media modeling with machine learning to assess and predict lake chlorophyll a concentrations

Eutrophication and excessive algal growth pose a threat on aquatic organisms and the health of the public, environment, and the economy. Understanding what drives excessive algal growth can inform mitigation measures and aid in advance planning to minimize impacts. We demonstrate how simulated data from weather, hydrological, and agroecosystem numerical prediction models can be combined with machine learning (ML) to assess and predict chlorophyll a (chl a) concentrations, a proxy for lake eutrophication and algal biomass. The study area is Lake Erie for a 16-year period, 2002–2017. A total of 20 environmental variables from linked and coupled physical models are used as input features to train the ML model with chl a observations from 16 measuring stations. Included are meteorological variables from the Weather Research and Forecasting (WRF) model, hydrological variables from the Variable Infiltration Capacity (VIC) model, and agricultural management practice variables from the Environmental Policy Integrated Climate (EPIC) agroecosystem model. The consolidation of these variables is conducive to a successful prediction of chl a. Aside from the synergistic effects that weather, hydrology, and fertilizers have on eutrophication and excessive algal growth, we found that the application of different forms of both P and N fertilizers are highly ranked for the prediction of chl a concentration. The developed ML model successfully predicts chl a with a coefficient of determination of 0.81, bias of −0.12 μg/l and RMSE of 4.97 μg/l. The developed ML-based modeling approach can be used for impact assessment of agriculture practices in a changing climate that affect chl a concentrations in Lake Erie.     

Otolith microchemistry shows natal philopatry of walleye in western Lake Erie

Natal philopatry is important to the structure of fish populations because it can lead to local adaptations among component stocks of a mixed population, reducing the risk of recruitment failure. By contrast, straying between component stocks may bolster declining populations or allow for colonization of new habitat. To examine rates of natal philopatry and straying among western Lake Erie walleye (Sander vitreus) stocks, we used the concentration of strontium [Sr] in otolith cores to determine the natal origin of adults captured at three major spawning sites: the Sandusky (n = 62) and Maumee (n = 55) rivers and the Ohio reef complex (n = 50) during the 2012–2013 spawning seasons. Mean otolith core [Sr] was consistently and significantly higher for individuals captured in the Sandusky River than for those captured in the Maumee River or Ohio reef complex. Although logistic regression indicates that no individuals with a Maumee River or Ohio reef complex origin were captured in the Sandusky River, quadratic discriminant analysis suggests low rates of straying of fish between the Maumee and Sandusky rivers. Our results suggest little straying and high rates of natal philopatry in the Sandusky River walleye stock. Similar rates of natal philopatry may also exist across western Lake Erie walleye stocks, demonstrating a need for stock-specific management.     

Tributary use and large-scale movements of grass carp in Lake Erie

Infrequent captures of invasive, non-native grass carp (Ctenopharyngodon idella) have occurred in Lake Erie over the last 30+ years, with recent evidence suggesting wild reproduction in the lake’s western basin (WB) is occurring. Information on grass carp movements in the Laurentian Great Lakes is lacking, but an improved understanding of large-scale movements and potential areas of aggregation will help inform control strategies and risk assessment if grass carp spread to other parts of Lake Erie and other Great Lakes. Twenty-three grass carp captured in Lake Erie’s WB were implanted with acoustic transmitters and released. Movements were monitored with acoustic receivers deployed throughout Lake Erie and elsewhere in the Great Lakes. Grass carp dispersed up to 236 km, with approximately 25% of fish dispersing greater than 100 km from their release location. Mean daily movements ranged from <0.01 to 2.49 km/day, with the highest daily averages occurring in the spring and summer. The Sandusky, Detroit, and Maumee Rivers, and Plum Creek were the most heavily used WB tributaries. Seventeen percent of grass carp moved into Lake Erie’s central or eastern basins, although all fish eventually returned to the WB. One fish emigrated from Lake Erie through the Huron-Erie Corridor and into Lake Huron. Based on our results, past assessments may have underestimated the potential for grass carp to spread in the Great Lakes. We recommend focusing grass carp control efforts on Sandusky River and Plum Creek given their high use by tagged fish, and secondarily on Maumee and Detroit Rivers.     

Interacting effects of climate change and agricultural BMPs on nutrient runoff entering Lake Erie

Agricultural best management practices (BMPs) have been implemented in the watersheds around Lake Erie to reduce nutrient transfer from terrestrial to aquatic ecosystems and thus protect and improve the water quality of Lake Erie. However, climate change may alter the effectiveness of these BMPs by altering runoff and other conditions. Using the Soil and Water Assessment Tool (SWAT), we simulated various climate scenarios with a range of BMPs to assess possible changes in water, sediment, and nutrient yields from four agricultural Lake Erie watersheds. Tile drain flow is expected to increase as is the amount of sediment that washes from land into streams. Predicted increases in tributary water flow (up to 17%), sediment yields (up to 32%), and nutrient yields (up to 23%) indicate a stronger influence of climate on sediment compared to other properties. Our simulations found much greater yield increases associated with scenarios of more pronounced climate change, indicating that above some threshold climate change may markedly accelerate sediment and nutrient export. Our results indicate that agricultural BMPs become more necessary but less effective under future climates; nonetheless, higher BMP implementation rates still could substantially offset anticipated increases in sediment and nutrient yields. Individual watersheds differ in their responsiveness to future climate scenarios, indicating the importance of targeting specific management strategies for individual watersheds.     

Evaluating the spatial distribution and source of phthalate esters in the surface water of Xingkai Lake,China during summer

Increasing production and usage of phthalate esters (PAEs) has made them ubiquitous in the environment. In this study, the distribution and source of PAEs in the surface water of Xingkai Lake, China were analyzed. The concentration of ΣPAEs in the water of Xingkai Lake ranged from 0.26 to 3.83 μg/L with a median of 1.28 μg/L. It was observed that the difference in the concentration of ?PAEs between the small and large Xingkai Lakes is not significant (p > 0.05). Agriculturally dominated land use types in the Xingkai Lake watershed may be mainly responsible for the occurrence of PAEs in this Lake. The distribution of butyl benzyl phthalate (BBP) in small and large Xingkai Lakes showed a significant difference (p < 0.05) which may be related to anthropogenic activities. ?PAEs in the water of Xingkai Lake demonstrated significant positive correlations with the ratio of total nitrogen (TN) to concentration of TP (r_p = 0.697, p < 0.01) and the concentration of suspended particulate organic matter (SPOM) (r_p = 0.345, p < 0.05). These results further indicate that the concentration of nutrients from agricultural activity had an impact on the concentrations of PAE in the lakes. Furthermore, the more SPOM would lead to more suspension of PAEs in the water phase. The source analysis of PAEs showed that high molecular weight PAEs were dominant in the Xingkai Lake which may be arising from the combustion of plastics or from building materials and household furnishing.