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.     

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.     

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.     

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.     

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.     

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.     

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.     

Environmental Factors Controlling Physiological Changes in Cladophora in Lake Erie

Several physiological characteristics of Cladophora glomerata from eastern Lake Erie were monitored frequently during the summer of 1977. Soluble reactive phosphorus and nitrate-nitrogen in the lake water were also measured.Cladophora biomass generally increased throughout June, although there were periodic declines. In mid-July, biomass sharply decreased to a low level. Chlorophyll content tended to be high during periods of increasing biomass but was lower after each biomass decline. Changes in biomass did not correlate with changes in either phosphate-phosphorus or nitrate-nitrogen in the lake water. Cellular nitrogen levels fluctuated independent of lake water nitrate-nitrogen concentrations. Cellular nitrogen levels remained above the critical concentration, 1.1%-N. Luxury phosphorus levels were observed to increase following pulses of soluble orthophosphate in the lake water. Measurements of cellular total phosphorus indicate that levels remain well above the critical concentration of 0.06%-P. It is concluded that neither nitrogen nor phosphorus is limiting the growth of Cladophora at the sites sampled. The mid-summer die-off does not appear to be due to a simple nutrient deficiency.     

Effect of the urbanized embayment Toronto Harbour on the composition and production of zooplankton

To better understand zooplankton dynamics in Lake Ontario’s Toronto Harbour and adjacent coastal area (CA), we sampled zooplankton, phytoplankton, nutrients and physical parameters on six dates in 2016. Despite higher levels of nutrients, chlorophyll and primary production in the inner harbor (IH), the areas supported similar May to November zooplankton biomass (IH = 32 ± 7 and CA = 42 ± 10 mg/m³). IH values were much lower than other nutrient-enriched embayments in Lake Ontario, yet CA biomass was twice that of nearshore sites away from Toronto. Small zooplankton such as rotifers and Bosmina dominated IH; and large taxa (Daphnia, calanoids and predatory cladocerans) were more important in the CA. Daphnia, Bosmina, cyclopoids and calanoids were larger in the CA, and adult cyclopoids had higher egg ratios. This led to low annual IH production estimates for both cyclopoid and calanoid copepods. Total phosphorus and chlorophyll did not appear to regulate zooplankton biomass, but positive relationships were found with bacterial biomass in the IH and with temperature in the cool season. Atypically high fish planktivory rates likely suppressed larger IH zooplankton in 2016, allowing small, resilient Bosmina to flourish and contribute 84% of total production in the IH. Comparing 2016 data to previous zooplankton surveys revealed considerable inter-annual variation in proportions of Daphnia, Bosmina and predatory cladocerans over the 1994 to 2016 period, and the strong top-down controls observed in 2016 were not typical. Elevated microbial production may serve as an important alternate trophic pathway supporting cladoceran populations in Toronto Harbour.     

Factors affecting Cladophora growth in the eastern basin of Lake Erie: Analysis of a monitoring dataset (2012–2019)

Cladophora is a naturally occurring benthic alga in the Great Lakes which can reach nuisance levels in the nearshore, leading to beach closures and other impacts. A monitoring program was initiated in 2012 in the eastern basin of Lake Erie to identify ecological factors driving its growth. Inflows from the Grand River, the largest river to the north shore, were generally positively associated with phosphorus concentrations in the nearshore and negatively associated with light reaching the lakebed. At the depths sampled (3 m–18 m), Cladophora was strongly influenced by light availability, and due to shading by the Grand River plume, an overall negative association was found between Cladophora biomass and phosphorus inputs. Phosphorus limitation was only observed at shallow sites farthest from the Grand River. Positive associations between dreissenid mussel coverage and both Cladophora biomass and tissue phosphorus suggest that nutrient cycling by dreissenids supports Cladophora growth. Our results indicate that i.) the Grand River has a strong influence on nearshore nutrient levels and water clarity; and ii.) Cladophora is limited by both phosphorus and light to varying degrees within the study area, although light appears to be the dominant factor, at least at these depths, years, and locations. The implication that phosphorus reductions could lead to increased Cladophora biomass by improving light conditions will need to be considered carefully against the known historical success of controlling nuisance algae through nutrient management.     

Systemic,early-season Microcystis blooms in western Lake Erie and two of its major agricultural tributaries (Maumee and Sandusky rivers)

Recurrent, massive cyanobacterial blooms composed mainly of the genus Microcystis indicate a broad-scale re-eutrophication of Lake Erie. In the past, ameliorating eutrophication relied on intentionally decreasing point-source tributary nutrient, especially phosphorus, loads to the lake. However, recent research has shown that tributaries load not only nutrients but also bloom-levels of phytoplankton, including Microcystis. We built on this previous work by sampling earlier in the year and in much smaller tributaries in both the Maumee and Sandusky systems. We found Microcystis wet biomasses in these tributaries averaged 3.16 mg/L (± 0.59 mg/L, one standard error of the mean) in 2009 and 3.42 mg/L (± 0.55 mg/L) in 2010. Importantly, we found Microcystis in small ditches in March, much earlier than previously observed. Microcystis biomass did not directly correspond to measured phosphorus, chlorophyll, or phycocyanin concentrations likely reflecting complexities associated with lagged physiological responses and/or non-linear growth relationships. Consequently, our findings emphasize that Microcystis blooms form a more broad-scale problem than previously documented, occurring far upstream much earlier in the year.     

Distribution of nuisance Cladophora in the lower Great Lakes: Patterns with land use, near shore water quality and dreissenid abundance

Selected shorelines and offshore shoals in Lakes Erie, Huron and Ontario were surveyed with a high frequency hydroacoustic system to investigate current spatial patterns of nuisance benthic filamentous algal (e.g., Cladophora) cover and stand height. Cladophora reached nuisance levels at all sites in Lakes Erie and Ontario, but not in Lake Huron or Georgian Bay. Despite clear gradients in coastal land cover, near shore water quality gradients were generally weak, and for Lakes Erie and Ontario, measures of near shore water quality were similar to that at offshore shoals. Hierarchical partitioning analysis suggested that while dreissenid mussel abundance appeared to be important in determining the magnitude of Cladophora standing crop, the joint contribution of catchment land cover, near shore water quality (nutrient levels and suspended matter) and dreissenid mussel abundance explained nearly 95% of the total variance in nuisance Cladophora standing crop observed in this study. Although the results from this study are necessarily correlative in nature and definition of causal relationships is not possible, these results provide corroborating evidence from sites across a gradient within and across the lower Great Lakes that is consistent with the operation of the near shore shunt model.     

The Wall of Green: The Status of Cladophora glomerata on the Northern Shores of Lake Erie's Eastern Basin, 1995–2002

The biomass, areal coverage, algal bed characteristics, and tissue phosphorus concentrations of Cladophora glomerata were measured at 24 near shore rocky sites along the northern shoreline of Lake Erie's eastern basin between 1995–2002. Midsummer areal coverage at shallow depths (≤ 5 m) ranged from 4–100%, with a median value of 96%. Cladophora biomass began accumulating at most sites during early May, and achieved maximum values by mid-July. Peak seasonal biomass ranged from < 1 to 940 g/m² dry mass (DM), with a median value of 171 g/m² DM. Nearshore water concentrations of total phosphorus (TP) were lower than during pre-phosphorus abatement years. However, Cladophora biomass levels were similar to reported values in those years. The midsummer “die off” occurred shortly after the biomass peak, when water temperatures neared 22.5°C. Areal coverage declined after die-off to < 10%, mean filament lengths declined from 33 cm to < 1 cm, and mean biomass declined to < 1 g DM/m². Tissue phosphorus varied seasonally, with initial high values in early May (0.15 to 0.27% DM; median 0.23% DM) to midsummer seasonal low values during peak biomass (0.03 to 0.23% DM; median 0.06% DM). Cladophora biomass is sensitive to changes in phosphorus and light availability, and reductions in biomass previously achieved through phosphorus control may now be reversed because of increased water transparency and phosphorus availability to the benthos following establishment of dreissenids.     

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 2. Phosphorus Uptake Kinetics

Laboratory experiments were conducted with field populations of Cladophora glomerata to examine the phosphorus uptake process. Results from 35 experiments conducted over two field seasons emphasize the importance of two factors in regulating phosphorus uptake: dissolved phosphorus concentration and internal phosphorus pool size. The phosphorus uptake rate increases as dissolved phosphorus availability increases. Negative feedback on uptake rate by internal phosphorus pool size reduces the maximum phosphorus uptake rate as internal pools approach saturation. The absolute maximum phosphorus uptake rate for Cladophora was 4.5%P/day. Values for the half-saturation constant for uptake varied with internal phosphorus pool size and ranged between 30 and 250 μgP/L. The data were fit to published mathematical expressions which describe uptake as a function of internal and external phosphorus levels. The expressions may be used in mathematical models simulating the growth of Cladophora.     

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.     

Re-eutrophication of Lake Erie: Correlations between tributary nutrient loads and phytoplankton biomass

Both abiotic and biotic explanations have been proposed to explain recent recurrent nuisance/harmful algal blooms in the western basin and central basin of Lake Erie. We used two long-term (> 10 years) datasets to test (1) whether Lake Erie total phytoplankton biomass and cyanobacterial biomass changed over time and (2) whether phytoplankton abundance was influenced by soluble reactive phosphorus or nitrate loading from agriculturally-dominated tributaries (Maumee and Sandusky rivers). We found that whereas total phytoplankton biomass decreased in Lake Erie's western basin from 1970 to 1987, it increased starting in the mid-1990s. Total phytoplankton and cyanobacterial seasonal (May–October) arithmetic mean wet-weight biomasses each significantly increased with increased water-year total soluble reactive phosphorus load from the Maumee River and the sum of soluble reactive phosphorus load from the Maumee and Sandusky rivers, but not for the Sandusky River alone during 1996–2006. During this same time period, neither total phytoplankton nor cyanobacterial biomass was correlated with nitrate load. Consequently, recently increased tributary soluble reactive phosphorus loads from the Maumee River likely contributed greatly to increased western basin and (central basin) cyanobacterial biomass and more frequent occurrence of harmful algal blooms. Managers thus must incorporate the form of and source location from which nutrients are delivered to lakes into their management plans, rather than solely considering total (both in terms of form and amount) nutrient load to the whole lake. Further, future studies need to address the relative contributions of not only external loads, but also sources of internal loading.