What is the Limiting Nutrient in Winter in Urban Reservoirs? A Case Study.

The importance of reservoirs in widely acknowledged by urban population, yet little is understood scientifically about their ability to process nutrients deposited into them in winter. Nutrients in waste water, lawns and construction runoff are deposited into reservoirs and several ecosystem services are lost which leads to what several researchers call “the urban syndrome”. Some studies have been done on the winter limnology of lakes, yet little is understood about the same process in reservoirs. To fill this missing knowledge gap, a study on one of Nebraska’s lakes (Holmes’ lake) was done. In this study, we simulated how phosphorus, nitrogen and trace nutrients addition would influence this lake’s phytoplankton growth in winter. We found that adding nutrients in a combination significantly increased gross primary production (p\u3c0.1 in the Phosphorous+ Trace element treatment) and net primary production. In single nutrient additions we visually observed higher GPP, NPP in phosphorous and trace elements though this was not statistically significant. In this study we observed that addition of nutrients had no significant influence on extracellular respiration. These results provide ample evidence to suggest that phytoplankton activity continues in winter and Holmes’ lake is nutrient co-limited. Advisor: Dr. Jessica Corma

What is the Winter Limiting Nutrient in Urban Reservoirs? A Case study.

The importance of reservoirs is widely acknowledged by urban populations, yet little is understood scientifically about their ability to process nutrients deposited into them in winter. For example, when agricultural runoff is deposited in lakes in winter or any other season, eutrophication might arise in the spring. With increased eutrophication, several ecosystem services are lost and this leads to what several researchers call “the urban syndrome”. Some studies have been done on the winter limnology of lakes, yet little is understood about the above in reservoirs. The sustainability of urban reservoirs relies on understanding how the phytoplankton in urban reservoirs interacts with increased nutrients in winter and how that affects other ecosystem services provided reservoirs in other seasons currently and long term. To fill this missing knowledge gap, we studied one of Nebraska’s lakes (Holmes’ lake) was done. In this study, we simulated how nutrient addition would influence this lake’s phytoplankton growth in winter. To assess this, we added nutrients to collected lake water and used non-invasive sensing PreSens to measure dissolved oxygen. The collected data was used to find Net primary production (NPP), gross primary production (GPP), and extracellular respiration (ER) under different nutrient treatments. We found that adding more than one nutrient significantly increased gross primary production (Pr\u3ef= 0.0017446) in the Phosphorous+ Trace element treatment. A similar trend was observed in Net Primary production. However, the addition of either of the nutrients had no significant influence on extracellular respiration. These results provide ample evidence to suggest the presence of nutrient co-limitation in winter in urban reservoirs namely Holmes’ lake. It is also important to note that contrary to the expectation, the reservoir\u27s phytoplankton community remains active and responsive even in the cold of winter. Advisor: Jessica Corma

What is the Limiting Nutrient in Winter in Urban Reservoirs? A Case Study.

The importance of reservoirs in widely acknowledged by urban population, yet little is understood scientifically about their ability to process nutrients deposited into them in winter. Nutrients in waste water, lawns and construction runoff are deposited into reservoirs and several ecosystem services are lost which leads to what several researchers call “the urban syndrome”. Some studies have been done on the winter limnology of lakes, yet little is understood about the same process in reservoirs. To fill this missing knowledge gap, a study on one of Nebraska’s lakes (Holmes’ lake) was done. In this study, we simulated how phosphorus, nitrogen and trace nutrients addition would influence this lake’s phytoplankton growth in winter. We found that adding nutrients in a combination significantly increased gross primary production (p\u3c0.1 in the Phosphorous+ Trace element treatment) and net primary production. In single nutrient additions we visually observed higher GPP, NPP in phosphorous and trace elements though this was not statistically significant. In this study we observed that addition of nutrients had no significant influence on extracellular respiration. These results provide ample evidence to suggest that phytoplankton activity continues in winter and Holmes’ lake is nutrient co-limited. Advisor: Dr. Jessica Corma

What is the Winter Limiting Nutrient in Urban Reservoirs? A Case study.

The importance of reservoirs is widely acknowledged by urban populations, yet little is understood scientifically about their ability to process nutrients deposited into them in winter. For example, when agricultural runoff is deposited in lakes in winter or any other season, eutrophication might arise in the spring. With increased eutrophication, several ecosystem services are lost and this leads to what several researchers call “the urban syndrome”. Some studies have been done on the winter limnology of lakes, yet little is understood about the above in reservoirs. The sustainability of urban reservoirs relies on understanding how the phytoplankton in urban reservoirs interacts with increased nutrients in winter and how that affects other ecosystem services provided reservoirs in other seasons currently and long term. To fill this missing knowledge gap, we studied one of Nebraska’s lakes (Holmes’ lake) was done. In this study, we simulated how nutrient addition would influence this lake’s phytoplankton growth in winter. To assess this, we added nutrients to collected lake water and used non-invasive sensing PreSens to measure dissolved oxygen. The collected data was used to find Net primary production (NPP), gross primary production (GPP), and extracellular respiration (ER) under different nutrient treatments. We found that adding more than one nutrient significantly increased gross primary production (Pr\u3ef= 0.0017446) in the Phosphorous+ Trace element treatment. A similar trend was observed in Net Primary production. However, the addition of either of the nutrients had no significant influence on extracellular respiration. These results provide ample evidence to suggest the presence of nutrient co-limitation in winter in urban reservoirs namely Holmes’ lake. It is also important to note that contrary to the expectation, the reservoir\u27s phytoplankton community remains active and responsive even in the cold of winter. Advisor: Jessica Corma

Three years of cover crops management increased soil organic matter and labile carbon pools in a subtropical vegetable agroecosystem

Abstract Cover crops have been widely adopted to improve soil functions in agroecosystems, including providing carbon (C) inputs that can contribute to soil C sequestration. However, soil C changes may be slow after introducing cover crops in unfavorable environments for soil organic matter (SOM) accumulation, like the Southeast United States subtropical region characterized by a warm humid climate, and coarse‐textured soils. We examined labile C pools as potential early indicators of SOM changes after cover crop introduction in a sandy subtropical vegetable production system. We compared the effects of four cover crop monocultures namely two grasses [sorghum sudangrass, Sorghum bicolor × S bicolor var. Sudanese and pearl millet, Pennisetum glaucum (L.) R. Br.], two legumes (sunn hemp, Crotalaria juncea L., and cowpea, Vigna unguiculata Walp.), and one four‐species mixture on soil organic carbon pools for 3 years. Soil samples were collected at a 15‐cm depth before cover crop planting and post cover crop incorporation to assess changes in SOM, permanganate‐oxidizable carbon (POX‐C), mineralizable carbon (Cmin), and water extractable organic carbon (WEOC). The incorporation of cover crops increased concentrations of SOM, POX‐C, and Cmin in year 3 relative to their baseline values in year 1. Concentration of SOM increased by 0.24 ± 0.05% (mean ± standard error) after 3 years of cover crop management. However, concentrations of WEOC significantly decreased in years 2 and 3 relative to the baseline. Monocultures and the mixture had similar effects on measured C pools, likely due to comparable aboveground biomass production. Our findings highlight the potential of POX‐C and Cmin as early indicators of SOM accumulation driven by cover crops use, as well as the capacity of cover crops to build SOM in similar subtropical systems and coarser textured soils