Lake morphometry underlies physical and chemical parameters affecting the distribution of phytoplankton functional groups in lakes of the Sakarya River Basin (Turkey)

To test the effects of lake morphometry (lake size and depth) on water quality parameters which affect the phytoplankton functional groups (FG) distribution, phytoplankton and some environmental parameters were sampled in November 2017 and May 2018 at the two or three monitoring stations in nine Lakes of Sakarya River Basin (Turkey). Lake size and depth affected phytoplankton FG distribution in both large-sized and small-sized lakes by affecting light availability which was mainly driven by the mixing events during the studied period. Al- though PO4 -P and alkalinity were the other main environmental constraints influencing phytoplankton distribution, they were not directly affected by lake morphometry. Codon Lo was mainly found in small-sized and shallow lakes, whereas coda B, C, D, J, R, and T, which do not have active buoyancy regulation and adapt to high Zmix/Zeu con- ditions, occurred with high relative biovolume in large-sized water bodies.

The Relationship of Lake Morphometry and Phosphorus Dynamics of a Tropical Highland Lake: Lake Tana, Ethiopia

Lakes hold most of the world’s fresh surface water resources. Safeguarding these resources from water quality degradation requires knowledge of the relationship between lake morphometry and water quality. The 3046-km2 Lake Tana in Ethiopia is one of the water resources in which the water quality is decreasing and water hyacinths have invaded. The objective of this study is to understand the interaction between the lake morphometry and water quality and specifically the phosphorus dynamics and their effect on the water hyacinths. A bathymetric survey was conducted in late 2017. Various morphometric parameters were derived, and both these parameters and sediment available phosphorus were regressed with the dissolved phosphorus. The results show that, with a wave base depth that is nearly equal to a maximum depth of 14.8 m, the bottom sediments were continuously suspended in the water column. As a result of the resuspension mixing, we found that the dissolved phosphorus in the water column decreased with lake depth and increased with sediment available phosphorus (R2 = 0.84) in the northern half of the lake. This relationship is not as strong in the south due to a large flow of Gilgel Abay to the outlets. Water hyacinths were found where the lake was shallow and the available phosphorus was elevated. The large reservoir of sediment phosphorus will hamper any remedial efforts in removing the water hyacinths.

Methane emissions from lakes in the Alpine region: insights from two years of mobile eddy covariance flux measurements

<p>Lakes are considered an important natural source of methane (CH<sub>4</sub>). However, direct measurements of lake-atmosphere gas exchange are still sparse especially in the Alpine region. To overcome this shortcoming, we designed a mobile eddy covariance (EC) station to measure CO<sub>2</sub>, CH<sub>4</sub>, and energy fluxes at various lakes in the Alps. EC measurements were compared to flux measurements using floating chambers and related to abiotic and biotic factors like temperature, lake morphometry, dissolved components and trophic status.</p><p>During the first year, measurements were conducted at 9 lakes at different elevations ranging from 200 to 1900 m.a.s.l. to capture the spatial variability. The following year, measurements were repeated more frequently at three contrasting lakes to capture the seasonal trends of the fluxes.</p><p>The results indicate that all lakes were supersaturated with CH<sub>4</sub>. However, there was a high variability in the magnitude of CH<sub>4</sub> emissions between lakes with generally higher emissions from warmer lakes at low elevation. In particular, the lake at the lowest elevation, Lake Caldaro, had highest dissolved CH<sub>4</sub> concentrations and emissions and showed a clear seasonal trend with emissions peaking during the hot summer months. In contrast, the lake at the highest elevation, Lake Zoccolo, showed low CH<sub>4</sub> concentrations and emissions with highest concentrations in fall when the water level was low.</p>

Meteorological and Nutrient Conditions Influence Microcystin Congeners in Freshwaters

Cyanobacterial blooms increasingly impair inland waters, with the potential for a concurrent increase in cyanotoxins that have been linked to animal and human mortalities. Microcystins (MCs) are among the most commonly detected cyanotoxins, but little is known about the distribution of different MC congeners despite large differences in their biomagnification, persistence, and toxicity. Using raw-water intake data from sites around the Great Lakes basin, we applied multivariate canonical analyses and regression tree analyses to identify how different congeners (MC-LA, -LR, -RR, and -YR) varied with changes in meteorological and nutrient conditions over time (10 years) and space (longitude range: 77°2′60 to 94°29′23 W). We found that MC-LR was associated with strong winds, warm temperatures, and nutrient-rich conditions, whereas the equally toxic yet less commonly studied MC-LA tended to dominate under intermediate winds, wetter, and nutrient-poor conditions. A global synthesis of lake data in the peer-reviewed literature showed that the composition of MC congeners differs among regions, with MC-LA more commonly reported in North America than Europe. Global patterns of MC congeners tended to vary with lake nutrient conditions and lake morphometry. Ultimately, knowledge of the environmental factors leading to the formation of different MC congeners in freshwaters is necessary to assess the duration and degree of toxin exposure under future global change.

Thermal preference influences depth use but not biomass of predatory fishes in response to lake morphometry

ABSTRACTTop predators’ responses to environmental conditions shape food web architecture and influence ecosystem structure and stability. Yet the impacts of fundamental properties like ecosystem size and morphometry on top predators’ behaviour are poorly understood. We examined how lake morphometry impacts the behaviour (inferred by depth use) of three key fish top predators—the cold-adapted lake trout, the cool-adapted walleye, and the warm-adapted smallmouth bass— which can each strongly impact local food web structure. We used catch-per-unit-effort data from nearly 500 boreal lakes of Ontario, Canada to evaluate the role of thermal preference in dictating mean depth of capture and biomass index in response to lake morphometry. We found evidence that thermal preferences influence how species’ depth use and biomass changed with lake size, proportion of littoral area, and maximum lake depth, although we found no relationship with lake shape. However, found no strong evidence that lake morphology influences these species’ biomasses, despite theory that predicts such a relationship. Our results suggest that some aspects of lake morphometry can alter habitat accessibility and productivity in ways that influence the behaviour and biomass of these top predator species depending on their thermal preferences. Our results have implications for how lake food webs expand and contract with lake morphometry and other key abiotic factors. We argue that several key abiotic factors likely drive top predator depth use in ways that may shape local food web structure and play an important role in determining the ultimate fate of ecosystems with environmental change.