Steinman A, Abdimalik M, Ogdahl ME, Oudsema M. 2016. Understanding planktonic vs. benthic algal response to manipulation of nutrients and light in a eutrophic lake. Lake Reserve Manage. 32:402–409. We examined the environmental factors influencing the growth of benthic and planktonic algae in Lake Macatawa, a hypereutrophic lake located in west Michigan. Turbidity may limit planktonic growth in the main body of the lake, despite high P concentrations, whereas shallow water depths in the littoral regions of the lake may allow benthic algal growth. We experimentally amended nutrients to benthic algae using nutrient diffusing substrates near the sediment surface and to phytoplankton using nitrogen (N) and phosphorus (P) spikes into 10 L carboys suspended from a PVC-constructed frame near the water surface to test how nutrient and light regimes influence these potentially competing autotrophic communities. Benthic algae were co-limited by N and P, whereas phytoplankton were P-limited. The N-only treatments resulted in negative algal growth. In addition, microcystin concentration (phytoplankton only) also responded positively to P additions and negatively to N-only treatments. We speculate that much of the P in this lake is bound to sediment and not bioavailable, so despite the high total P concentrations, the algae are P-limited at certain times of the year. Irradiance levels did not seem to be photosynthetically limiting during this study. Our results have management implications: (1) use of TP as an indicator of P limitation may be flawed without concomitant measurement of bioavailable P; and (2) control of external P loading is critical to directly limit phytoplankton abundance but also can result in indirect control of benthic algae if internal P loading from the sediment is a key source of P to this community.

Reducing nonpoint source pollution is an ongoing challenge in watersheds throughout the world. Implementation of best management practices, both structural and nonstructural, is the usual response to this challenge, with the presumption that they are effective. However, monitoring of their efficacy is not a standard practice. In this study, we evaluate the effectiveness of two wetland restoration projects, designed to handle runoff during high flow events and serve as flow-through retention basins before returning flow further downstream. The Macatawa Watershed is located in west Michigan, is heavily agricultural, and drains into Lake Macatawa, a hypereutrophic lake with total phosphorus concentrations usually exceeding 100 µg/L. We measured turbidity, total phosphorus, and soluble reactive phosphorus both upstream and downstream of these wetland complexes during base flow and storm events. While both turbidity and phosphorus increased significantly during storm events compared to baseflow, we found no significant difference in upstream vs. downstream water quality two years following BMP construction. We also measured water quality in Lake Macatawa, and found the lake remained highly impaired. Possible reasons for the lack of improved water quality: (1) The restored wetlands are too young to function optimally in sediment and phosphorus retention; (2) the scale of these BMPs is too small given the overall loads; (3) the locations of these BMPs are not optimal in terms of pollutant reduction; and (4) the years following postconstruction were relatively dry so the wetlands had limited opportunity to retain pollutants. These possibilities are evaluated.

Steinman AD, Hassett MC, Oudsema M, Rediske R. 2018. Alum efficacy 11 years following treatment: phosphorus and macroinvertebrates. Lake Reserv Manage. 34:167—181. Internal phosphorus loading and benthic macroinvertebrate community structure were analyzed at 4 sites in Spring Lake, Michigan, ˜11 yr following an alum treatment. Phosphorus (P) release rates, benthic macroinvertebrate community structure, sediment chemistry, and water quality variables (total dissolved solids, pH, dissolved oxygen, water clarity) were compared to measurements taken previously (2003/2004: pre-alum application, 2006: 8 mo post-alum application, and 2010: 5 yr post-alum application) at the same sites and using comparable methods. Total phosphorus (TP) concentrations in surface water samples from 2016 (38—45 νg/L) were similar to those measured in 2006 and 2010 (20—80 νg/L) at all sites; however, 2016 TP concentrations in the near-bottom water at the 2 deeper sites were elevated (˜250 and 1,000 νg/L, respectively) compared to TP concentrations of <60 νg/L in 2006 and 2010, suggesting internal loading may be increasing, at least at these 2 sites. In contrast, maximum P release rates from the 2016 sediments were similar to or lower than 2010 rates, and an order of magnitude lower than before alum was applied. Phosphorus content in the sediment was fractionated; loosely sorbed sediment SRP concentrations were very low at all sites. Macroinvertebrate community was similar in density and composition to the 2010 results. These results are suggestive, but not conclusive, that internal P loading is increasing in parts of Spring Lake. Alum application can serve as an effective short-term solution to the longer-term problem of internal P loading, but its effectiveness is critically tied to concurrent reductions in external P loading.