On the Role of a Large Shallow Lake (Lake St. Clair, USA‐Canada) in Modulating Phosphorus Loads to Lake Erie

Abstract

It is often assumed that large shallow water bodies are net sediment nondepositional annually and that if they have nutrient loads from multiple sources, those loads are quickly homogenized before exiting the water bodies. Where this is not the case, it impacts understanding and predicting consequences of nutrient load reductions, both for the water body and for those downstream of it. We applied a threedimensional ecological model to a large shallow lake, Lake St. Clair (US/Canada), to quantify the total and dissolved reactive phosphorus (TP and DRP) transport and retention, and construct tributary-specific relationships between phosphorus load to the lake and the amount of phosphorus that leaves the lake for the three major tributaries. Lake St. Clair is situated between the St. Clair and Detroit rivers, the latter enters Lake Erie. Efforts to reduce Lake Erie's re-eutrophication requires an understanding of nutrient transport and retention in each of its subwatersheds including those that feed indirectly via Lake St. Clair. We found that over the simulation period, the lake retained a significant portion of TP (17%) and DRP (35%) load and that TP and DRP retention was spatially variable and largely controlled by a combination of lake depth, resuspension, and plankton uptake. Compared to the Clinton and Sydenham rivers, the Thames River contributed a larger proportion of its load to the lake's outflow. However, because the lake's load is dominated by the St. Clair River, 40% reductions of nutrients from those subwatersheds will result in less than a 5% reduction in the load to Lake Erie. Key Points:• A large shallow lake with a 9 day water retention time still retains 17% of its total phosphorus and 35% of its dissolved phosphorus inputs • Tributary loads are not well-mixed within the lake, leading to spatial-temporal differences in phosphorus retention • While wind-induced resuspension drives interannual variability in phosphors retention, depths greater than 5 m are net depositional Supporting Information:• Supporting Information S1

High Sensitivity of Lake Hypoxia to Air Temperatures, Winds, and Nutrient Loading: Insights From a 3‐D Lake Model

“…The simulated effects of altered air temperature and wind speed were largely as expected, with warmer temperatures and weaker winds exacerbating hypoxia and anoxia. The results supported previous findings that variations of climatic air temperature are of comparable importance to changes in nutrient loads (Bocaniov et al, 2016, 2017, 2019; Bocaniov & Scavia, 2016; Del Giudice et al, 2018). The model outcomes give the first evidence that changes in ice cover are an important state change that will likely amplify the otherwise linear and proportional response of hypoxia to air temperature over the expected range of 21st century values.…”

Spatio-temporal connectivity of the aquatic microbiome associated with cyanobacterial blooms along a Great Lake riverine-lacustrine continuum

“…Amongst all tributaries discharging into Lake Erie, the Thames River ranks 3 rd behind the Maumee and Sandusky Rivers in contributing TP and SRP to Lake Erie ( Maccoux et al, 2016 ; Figure 1 ). Although the largest annual hydrological loads to Lake St. Clair come from the St. Clair River (average 2016–2019 discharge of 6,122 m 3 /s), which flows directly from Lake Huron, the Thames River has a disproportionate effect on the TP load, to the extent that P reduction in the Thames River basin will be more effective in reducing the P export from Lake St. Clair than from the equivalent in-flow Sydenham or Clinton Rivers ( Bocaniov et al, 2019 ). Lake St. Clair has a water residence time of ~9 days, and due to it shallow depth, is subjected to frequent vertical mixing, yet nutrient loads from its tributaries are not homogeneously mixed and vary seasonally and spatially ( Bocaniov et al, 2019 ).…”

“…Although the largest annual hydrological loads to Lake St. Clair come from the St. Clair River (average 2016–2019 discharge of 6,122 m 3 /s), which flows directly from Lake Huron, the Thames River has a disproportionate effect on the TP load, to the extent that P reduction in the Thames River basin will be more effective in reducing the P export from Lake St. Clair than from the equivalent in-flow Sydenham or Clinton Rivers ( Bocaniov et al, 2019 ). Lake St. Clair has a water residence time of ~9 days, and due to it shallow depth, is subjected to frequent vertical mixing, yet nutrient loads from its tributaries are not homogeneously mixed and vary seasonally and spatially ( Bocaniov et al, 2019 ). Lake St. Clair has also been shown to be a sink for nutrients retaining up to 20% of the TP load ( Bocaniov et al, 2019 ; Scavia et al, 2019 ), but altogether with loads from Canada and the US still contributes up to 41% of the annual TP load to Lake Erie’s Western Basin via the Detroit River (average 2016–2019 discharge of 6,383 m 3 /s), which is the second in importance after the Maumee River which contributes up to 48% ( Scavia et al, 2016 ).…”

Spatio-temporal dynamics of bacterial communities in the shoreline of Laurentian great Lake Erie and Lake St. Clair’s large freshwater ecosystems

“…[ 18 ], as well as habitat variation [ 14 ], among sampling locations, are strong drivers of the spatial variation of the microbial communities. We did not measure abiotic parameters such as nutrient levels at our sampling locations; however, due to the connectivity of the two lakes by the Detroit River [ 19 ], the short distances among the sampling locations and the eutrophication of Lake Erie [ 5 ] and St. Clair [ 20 ], our sampling locations might have similar habitat features which consequently resulted in the little spatial variation of the BCCs in our study. The chao 1 index of CB was higher than other sampling sites, potentially due to presence of more greenhouse agriculture area and consequently higher bioavailability of nutrients; however, more studies are needed to address the influence of greenhouse agriculture area on BC diversity.…”