Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 5. Model Development and Calibration

The development of a mathematical model for calculating the spatial distribution and temporal variation in Cladophora biomass and selected forms of phosphorus at a site on Lake Huron is described. The model is intended for use in evaluating the utility of various phosphorus management strategies in reducing the nuisance growth of Cladophora in the Great Lakes. The model is composed of a transport component which accounts for bulk transfer and exchange of phosphorus within the system and a kinetic component which describes chemical and biological reactions. The kinetic component includes the effects of light, temperature, and internal phosphorus levels on Cladophora growth rate, aspects of phosphorus uptake, and the impact of sloughing and self-shading on standing crop. The numerical value of coefficients associated with kinetic equations have been independently determined through laboratory studies.The model has been calibrated to a data set collected in the vicinity of the Harbor Beach, Michigan, wastewater treatment plant. A satisfactory fit was achieved for model calculations and observed levels of Cladophora biomass, internal phosphorus, and soluble reactive phosphorus. The model has few degrees of freedom because the coefficient values were fixed from field and laboratory measurements. A standing crop of Cladophora biomass of 300 gDW/m² with an internal phosphorus level of 0.35%P was characteristic of stations in the vicinity of the nutrient source. Soluble reactive phosphorus levels fluctuated widely due to mixing of the effluent plume with offshore waters, but averaged approximately 30 μgP/L. A distinct spatial trend was observed with Cladophora biomass, internal phosphorus, and soluble reactive phosphorus decreasing with distance from the point source of nutrients. The opportunity for model verification by perturbation through phosphorus removal is discussed.     

The Use of Remote Sensing to Map the Areal Distribution of Cladophora Glomerata at a Site in Lake Huron

The areal distribution of the benthic alga Cladophora glomerata and the percent areal coverage of Cladophora within 45.8 m (150 ft) by 15.3 m (50 ft) model cells for a 2.8 km length of Lake Huron shoreline at Harbor Beach, Michigan, are determined by remote sensing techniques. Data were acquired on 21 July 1979, a calm, clear day over Lake Huron at an altitude of 305 m with an eleven-channel modular multispectral scanner mounted in a NASA C-131 aircraft. Cladophora is determined by a conventional maximum likelihood statistical supervised classification technique employing three of the scanner bands. An intensive field survey of the study site indicated that the computer classified imagery is representative of the Cladophora distribution at Harbor Beach. Classification accuracy is not determined because the site was not mapped by ground surveys. The percent of areal coverage of model cells by Cladophora ranges from 0% to 93%. Calculations based on these percentages indicate that the alga occupies an area of 38,704 m² at the study site. Overlapping flight lines resulted in duplicate measurements of many model cells. The reproducibility of results for these areas is good (R = 0.86 and standard error of estimate of 9.9%) when suitable well-defined Cladophora training sites are common to adjacent data sets. The reproducibility decreases in the absence of this condition.     

Cladophora,mass transport,and the nearshore phosphorus shunt

The nearshore phosphorus shunt hypothesis and the potential for mussels to excrete phosphorus sufficient to meet the growth requirements of Cladophora are now well accepted by scientists studying Great Lakes biogeochemistry. The response of algal growth to near bottom water column phosphorus concentrations and the interplay between excretion and mass transport in yielding those concentrations have, however, not been elucidated. Here we present soluble reactive phosphorus profiles from the near bottom environment of Lake Michigan at a site near Good Harbor Bay, Michigan, where both mussels and Cladophora were present. Soluble reactive phosphorus was observed to accumulate under quiescent conditions, establishing a concentration boundary layer (CBL), 5–15 cm thick, with near bottom concentrations on the order of 2–8 μg P/L. A one-dimensional model was applied to determine mass transport conditions mediating the transition from CBL formation to CBL destruction. Significant wave height (SWH) was used as an indicator of mass transport intensity, and it was determined that the formation/destruction transition occurred at a SWH of 0.2 m at the 8-m study site depth. The Great Lakes Cladophora Model was applied to determine the time intervals required to saturate (1 day with the CBL present) and deplete (14 days with the CBL absent) algal internal P stores. A review of SWH conditions at the study site indicated that a CBL would be expected to form at a frequency sufficient to support the phosphorus nutrition of Cladophora over the entire May to August interval.     

Phosphorus Uptake Dynamics as Related to Mathematical Modeling of Cladophora at a Site on Lake Huron

Cladophora is a significant symptom of eutrophication in Lakes Erie and Ontario and is a local problem associated with nutrient perturbations in Lakes Huron, Michigan, and Superior. This paper presents results of measurements of phosphorus uptake rates as a function of internal phosphorus levels by Cladophora growing near Harbor Beach, Michigan. Cladophora collected near the Harbor Beach wastewater treatment plant had high levels of internal phosphorus and low (or even negative) phosphorus uptake rates. Cladophora distant from the wastewater treatment plant had low internal phosphorus levels and rapid phosphorus uptake rates. The experimental results are discussed in terms of quantitative kinetic formulations which may be incorporated into mathematical models useful for predicting the response of Cladophora to alternative management and control strategies. Preliminary model simulations of Cladophora biomass, internal phosphorus, and external phosphorus are qualitatively similar to observed field data.     

Monitoring Cladophora Growth Conditions and the Effect of Phosphorus Additions at a Shoreline Site in Northeastern Lake Erie

A study to measure environmental conditions, Cladophora standing crop, internal nutrient levels, and the effect of the addition of phosphorus to Cladophora growth at a single location on the north shore in the eastern basin of Lake Erie is described. In 1979, the mean standing crop for depths 0.5–3 m was 431 gDW/m² as measured at the time of maximum standing crop in early July. Thereafter, the alga was sloughed and carried ashore causing a rapid decline in standing crop. These events coincided with the attainment of lake temperatures exceeding 20° C. Total phosphorus concentrations averaged about 18 μg P/L while soluble reactive phosphorus levels remained near the limit of detection. Stoichiometric ratios of nitrate nitrogen to soluble reactive phosphorus approximated 150:1, suggestive of phosphorus limited conditions. Internal phosphorus and nitrogen levels averaged about 0.06% and 1.80%, respectively. In 1980, phosphorus (0.34 kg/day) was discharged at the 0.5 m depth commencing July 19. No response was noted until the water temperature dropped below 20° C in September when a rapid regrowth occurred, apparently in response to the nutrient addition. It is concluded that Cladophora grows in response to available phosphorus in the eastern basin of Lake Erie and that limitation of this nutrient may be expected to reduce Cladophora growth.     

Seasonal Abundance Patterns of Diatoms on Cladophora in Lake Huron

Rocks bearing Cladophora were collected from May to November 1979 at two locations near Harbor Beach, Michigan, in Lake Huron to document seasonal patterns of epiphytic diatom abundance and diatom proportion of the Cladophora-epiphyte assemblage biomass in an area receiving effluent from a municipal wastewater treatment plant. Data were examined for evidence of interactions between epiphytic diatoms and Cladophora.Cladophora first appeared in May at which time epiphytic diatoms comprised about 30% of the Cladophora-epiphytic assemblage biomass. Cladophora growth was greatest in June and July, accumulating much faster than diatoms. Peak Cladophora-epiphyte assemblage biomass was maintained from July to September. Cladophora biomass apparently decreased after August while diatom abundance increased to a September maximum. Diatoms were responsible for the sustained peak of Cladophora-epiphyte assemblage biomass as diatoms comprised over 60% of the assemblage biomass in September. The Cladophora-epiphyte assemblage collapsed by October.Low diversity of the epiphytic diatom taxocene and low diatom proportion of the Cladophora-epiphyte assemblage biomass indicated Cladophora may have outcompeted diatom epiphytes during the June-July Cladophora growth pulse. Subsequently epiphytic diatoms may have enhanced Cladophora sloughing by shading and successful nutrient competition.     

Evidence of Natural Reproduction by Planted Lake Trout in Lake Michigan

Lake trout (Salvelinus namaycush) fry were captured in southeastern Lake Michigan for the first time since the species was reintroduced from hatchery stocks in 1965. Spawning apparently occurred in fall 1979 on newly placed limestone riprap covering recently constructed power plant intake and discharge pipelines. Eggs presumably hatched in late February–March, 1980, and 57 fry (22–43 mm total length) were collected April–June, 1980, and three fry (55–62 mm) were collected in August, 1980.     

Cladophora (green algae) and dreissenid mussels over a nutrient loading gradient on the north shore of Lake Ontario

Benthic algae, much of it the green alga Cladophora, blanket the nearshore lakebed of the north shore of Lake Ontario. Nearshore field studies in Toronto, Ajax, Oshawa and Cobourg in 2012 and 2013, and Toronto in 2015 examined the distribution of Cladophora over a nutrient gradient on the north shore of the lake. Concentrations of total phosphorus, dissolved phosphorus and total inorganic nitrogen in the water column decreased from west to east over the gradient corresponding with decreasing watershed development and size. However, high surface cover and nuisance levels of Cladophora biomass were found across the gradient, including the least developed study area where total phosphorus concentrations were similar to those in the open lake. The abundance of Dreissena, high in all areas, was measured concurrently with Cladophora biomass and correlated positively at depths of 6 to 10 m. External loading of phosphorus provides a basis for abatement of Cladophora; however, the influences of enrichment along the shoreline, internal loading at the lakebed and lake trophic status in sustaining growth remain obscure. Nuisance levels of Cladophora are not isolated to locations experiencing elevated external loading and should be viewed in the context of interacting area-specific and lake-wide nutrient supplies.     

The Great Lakes Cladophora Model: Development,testing, and application to Lake Michigan

A recent review of the Great Lakes Water Quality Agreement has concluded that while controls on phosphorus inputs to Lake Michigan achieved the desired effect in offshore waters, the nearshore region continues to suffer from elevated phosphorus levels. Failure to achieve trophic state goals in the nearshore is manifested in nuisance growth of Cladophora and attendant impacts on property owners, utilities, and the public health and welfare. This study focuses on a site in Lake Michigan near Milwaukee, Wisconsin, where nuisance growth of Cladophora and associated beach fouling occur regularly. A mechanistic model simulating Cladophora growth, suitable for guiding nutrient management in the Great Lakes nearshore, is presented. The model represents an update of the Canale and Auer framework, reflecting current understandings of Cladophora ecology and offering a user-friendly interface making the software more widely available to decision makers. This Great Lakes Cladophora Model (GLCM) is first validated for the Auer/Canale data set collected in 1979 at a site on Lake Huron and then for a data set developed in 2006 for a site on Lake Michigan. Model performance under the strikingly different forcing conditions (depth, light, phosphorus levels) characteristic of these two sites affirms the widespread applicability of the tool. The GLCM is then extended to examine the impacts of ecosystem perturbation (dreissenid colonization) on Cladophora growth and to future approaches to monitoring and management.     

Biomass and Distribution of Cladophora Glomerata in Relation to Some Physical-Chemical Variables at Two Sites in Lake Erie

Cladophora was collected from 0.25-m² quadrats on alternate weeks at two sites located in Lake Erie near Hamburg, New York, and Walnut Creek near Erie, Pennsylvania, between June and November 1979. Cladophora biomass and internal nutrients (total Kjeldahl nitrogen and total phosphorus) were determined. Water samples were analyzed for total phosphorus, soluble reactive phosphorus, nitrate + nitrite nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen. Temperature and Secchi disk transparency were also recorded.The peak standing crop for Cladophora was 211 gDW/m² (July) at the Hamburg site and 57 gDW/m² (July) at Walnut Creek. The depth distribution of Cladophora at the sample sites was influenced by wave activity and drifting sand. As a result of sand scouring at the shallower depths, Cladophora biomass generally was greatest at the 3-m depth.Reductions in Cladophora internal nutrients corresponded to decreased nutrients in the water. Cladophora detached from its substrate during periods when low internal nutrient levels were observed. Internal total phosphorus concentrations were low and approached the minimum cell quota (0.05–0.06% –P) most of the time. Soluble reactive phosphorus values were also low (1–4 μgP/L). Levels of soluble reactive phosphorus and internal total phosphorus were low and almost always limiting, and may be responsible for the low biomass values observed. In addition, internal total phosphorus levels showed a significant positive correlation with Cladophora biomass. Internal total nitrogen values were generally less than 1%-N at Walnut Creek and ammonia nitrogen measurements were near detection limits. Cladophora was nitrogen-limited at the Walnut Creek site during part of the study period. Nitrate + nitrite nitrogen showed a significant positive correlation with Cladophora biomass at that site.     

Colonization and Growth of Attached Algae at the Lake Michigan Water Line

Changes in populations of attached algae growing near the water line along the west shore of Lake Michigan were observed. Emphasis was placed on harbor populations with particular focus on the algae of Milwaukee Harbor during 1979 and 1980. Vertical zonation on rocks and harbor structures is documented and seasonal growth patterns and selected interrelationships are described. Of the three major filamentous algal forms present in this habitat, Bangia appears as a permanent resident, while Ulothrix may be considered a seasonal and opportunistic plant, responding rapdily to changes in water level. Cladophora is a perennial, but plants above a depth of approximately 30 cm tend to grow as annuals due to conditions of ice scour. It is suggested that seasonal and spatial variation in the abundance of particular species is related to the physical growth requirements of the species.     

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.     

Water Quality Modeling of Lake Michigan and Consideration of the Anomalous Ice Cover of 1976–1977

An intensive survey of water quality parameters was conducted on Lake Michigan during 1976 and 1977. A dynamic phytoplankton simulation model (MICH1) was developed to investigate the observed field data and to use in forecasting lake responses to various phosphorus loading scenarios. The 1977 data indicated that the southern basin of Lake Michigan lost up to 3 μg P/ L compared to concentrations observed in 1976. In an attempt to simulate this rapid depletion of phosphorus, MICH1 required an implicit representation of suspected effects of an extensive ice cover observed during the winter of 1976–77. This included increasing the net apparent settling rate eight fold during ice cover. A total phosphorus model (TPM) was used in conjunction with MICH1 ;for forecasting. These forecasts indicate a steady-state total phosphorus concentration of 7 μg P/ L, given a target load recommended by the 1978 Water Quality Agreement. The projected time to obtain 95% of steady-state response to a load change was 7–14 years.     

Great Lakes Cladophora in the 21st century: same algae—different ecosystem

Nuisance growth of the attached, green alga Cladophora was considered to have been abated by phosphorus management programs mandated under the Great Lakes Water Quality Agreement. The apparent resurgence of nuisance growth in Lakes Erie, Michigan and Ontario has been linked conceptually to ecosystem alterations engineered by invasive dreissenid mussels (Dreissena polymorpha and Dreissenabugensis). Here, we apply contemporary modeling tools and historical water quality data sets in quantifying the impact of long-term changes in phosphorus loading and dreissenid-mediated changes in water clarity on the distribution and production of Cladophora. It is concluded that reductions in phosphorus loading in the pre-dreissenid period achieved the desired effect, as model simulations were consistent with the biomass declines reported from the early 1970s to the early 1980s. These declines were, however, largely offset by dreissenid-driven changes in water clarity that extended the depth of colonization by Cladophora, increasing total production. We were not able to isolate and quantify the significance of dreissenid mediation of phosphorus cycling using the historical database. Phosphorus management remains the appropriate mechanism for reducing nuisance levels of Cladophora growth. The development of action plans will require an improved understanding of nearshore phosphorus dynamics such as might be obtained through regular monitoring of soluble reactive phosphorus levels, internal phosphorus content and Cladophora biomass in impacted nearshore regions of the Great Lakes.     

Precision of Ages Determined from Scales and Opercles for Yellow Perch Perca flavescens

Scales and opercles were used to age yellow perch Perca flavescens collected in 1989 from Lake Madison (South Dakota), Dauphin Lake (Manitoba), and southern Lake Michigan (Indiana). Three readers aged fish from Lake Madison and Dauphin Lake once and two readers aged fish from Lake Michigan twice. The coefficient of variation (CV) was calculated to compare precision. Ages determined from opercles were as precise as those from scales for fish from Lake Madison (CV = 0 for both structures), and more precise than ages from scales for fish from Dauphin Lake (CV_opercle = 14.0, CV_scale = 27.4, p < 0.001) and Lake Michigan (CV _opercle = 10.6, CV_scale = 13.9, p < 0.001). The high precision of scale and opercle ages for yellow perch from Lake Madison can be attributed to the fast growth rate of fish from that lake and also that only age 1 and 2 fish were aged. The greater precision of opercle ages in comparison to scale ages for Dauphin Lake and Lake Michigan yellow perch can be attributed to ease of recognition of false annuli on opercles as well as to difficulty in distinguishing between false and true annuli crowded on the edge of scales from mature, slower growing fish. Because true annuli are more easily recognized on opercles, ages determined from opercles may be more accurate than ages determined from scales for yellow perch growing at slow or moderate rates.     

Silica Regeneration Processes in Nearshore Southern Lake Michigan

The seasonal depletion of dissolved silica to levels that limit diatom production is particularly critical in Lake Michigan's nearshore zone where diatom biomass is greatest, and where silica regeneration from sediments is not well-understood. In our study, intact, medium-fine sand cores, collected from an 11 m deep site in nearshore Lake Michigan during July-August 1980, released soluble reactive silica (SRS) at a mean rate of 2,707 ± 122 (SE) μg Si cm^?2 yr^?1 when incubated in darkness and at 12° C. This measured SRS release was greater than a diffusive flux (270 ± 49 (90% C.I.) μg Si cm^?2 yr^?1) estimated from SRS pore water profiles and physical sediment properties. SRS release from individual cores was not correlated with abundance of most macroinvertebrates (chironomids, pisidiid clams, or oligochaetes). However, a significant (P < 0.05) and inverse relationship between SRS release and Pontoporeia hoyi densities implied that amphipods suppressed SRS release through mixing and burial of a surficial floe layer, where most dissolution of biogenic silica occurs. Moreover, SRS release rates measured from our coarse-grained nearshore sediments were comparable to rates reported for fine-grained offshore material and further implicate dissolution of surficial biogenic silica as the source of remineralized SRS. Because nearshore areas of Lake Michigan undergo strong seasonal variations in temperature and diatom production, and because significant riverine silica inputs exist, we cannot extrapolate our results on a lakewide, or season-long basis. The data, however, strongly imply that nearshore sediments are an important participant in the Lake Michigan silica cycle.     

New Records of Freshwater Sponges (Porifera) for Southern Lake Michigan

Four species of freshwater sponge were identified in southern Lake Michigan: Spongilla lacustris (Linneaus), Eunapius fragilis (Leidy), Ephydatia fluviatilis (Linneaus), and Ephydatia muelleri (Lieberkuhn). Samples were collected from artificial substrates in Calumet (IL), Hammond (IN), and Michigan City (IN) harbors and represent the first reports of sponges in these waters. Numerical densities for all species combined were as high as 698 sponge colonies/m² on the iron hull of the permanently moored 110-m-long ship Milwaukee Clipper in Hammond Harbor. These densities were lowest at 1-m depth and greater at 2- and 3-m depths. A positive correlation (r² = 0.74) was found between the density of sponge colonies and the angle of the hull as it changed from near vertical at the water line to overhanging at greater depth (toward the keel). Ephydatia muelleri was the most common species based on frequency of occurrence and percent surface area covered. Observations of epizoic growth of sponges on live zebra mussels (Dreissena polymorpha Pallas) suggest that an ecological interaction exists between these two groups of organisms on these artificial substrates.     

Fate of phosphorus from a point source in the Lake Michigan nearshore zone

Nutrient loading into Lake Michigan can produce algal blooms which in turn can lead to hypoxia, beach closures, clogging of water intakes, and reduced water quality. The Great Lakes Water Quality Agreement targets for Lake Michigan are 5600 MT annually for total phosphorus (TP) loading, 7 μg L^?1 lake-wide mean TP concentration, and a chlorophyll-a concentration of 1.8 μg L^?1. However, in light of the recent resurgence of nuisance algal (Cladophora sp.) growth in the nearshore zone, the validity of these targets is now uncertain. The occurrence and abundance of Cladophora in the nearshore area depends primarily on the availability of dissolved phosphorus, light, and temperature. The availability of dissolved phosphorus is a potentially useful indicator of nearshore areas susceptible to excessive Cladophora growth and impaired water quality. Regulating agencies are looking for guidance in determining phosphorus loading rates that minimize local exceedance of the lake target concentration. In this study, the lake assimilative capacity was quantified by applying a biophysical model to estimate the area required for mixing and diluting wastewater treatment plant outfall TP loadings to the level of the lake target concentration during the Cladophora growing season. Model results compared well with empirical measurements of particulate and dissolved phosphorus as well as Cladophora biomass and phosphorus content. The model was applied to test scenarios of wastewater treatment plant phosphorus loading in two different years, in order to help establish phosphorus discharge limits for the plant.     

Microbial investigations of water,sediment, and algal mats in the mixed use watershed of Saginaw Bay,Michigan

Beach monitoring often includes testing for a single fecal indicator organism in the swimmable waters. Here, sediment, algae mat, shallow water, and deep water samples collected from four Saginaw Bay (Michigan, USA) beaches were tested for multiple fecal indicator organisms (Escherichia coli, enterococci, Clostridium perfringens, F + amp coliphage, and CN-13 coliphage) and molecular markers (human and bovine Bacteroides and enterococci surface protein) to determine the occurrence and sources of fecal indicator bacteria across beachscapes and characterize the environmental parameters which influence microbial water quality. Results show algae mats and sediment had higher levels of bacteria compared to surrounding water column. Higher concentrations of fecal indicators in shallow waters compared to deep water were attributed in part to sediment and algae bound bacteria and potential regrowth. Fecal indicator organisms were primarily influenced by wind, waves, and precipitation and partially identified as human specific using the enterococci surface protein gene. This project suggests the potential for sediment and algal mats to act as non-point sources of pollution in the nearshore zone. Future beach protection measures should focus on shallow water monitoring of multiple fecal indicators and beach grooming during calm morning hours.