Data_Sheet_2_Bioavailability of Dissolved Organic Phosphorus in Temperate Lakes.XLSX

<p>Freshwater aquatic systems are biogeochemical hotspots, with heterotrophic bacteria rapidly cycling the compounds that pass through them. P is a key nutrient that controls primary production in many freshwater ecosystems and is important for understanding eutrophication in lakes. Previous work has often focused on the dynamics of inorganic phosphorus and its impact on primary production, however, the role of nutrients bound in more complex organic forms (such as dissolved organic phosphorus, DOP) in supporting primary production and harmful algal blooms has been neglected. Here, we quantify the bioavailability of dissolved organic carbon (DOC) and DOP in 27 aquatic systems across the Upper Midwest United States. Using exponential decay models, long-term nutrient degradation assays revealed that decay constants for DOP ranged from −0.001 per day to −0.12 per day with a median value of −0.01 per day. These rates were geographically variable and were as high or higher than DOC decay constants, which ranged from −0.003 per day to −0.024 per day with a median value of −0.01 per day. Additionally, total bioavailability of DOP ranged from 0 to 100% with a median value of 78% of the DOP pool, demonstrating that DOP bioavailability was highly variable across systems. In contrast, bioavailable DOC was more tightly constrained with values ranging from 4.37 to 53.81% of the total DOC pool with a median value of 24.95%. DOP bioavailability was negatively correlated with the DOC:DOP of the organic matter pool, suggesting that bioavailable DOP is drawn down in systems that are more likely to be P limited. Finally, we show that including estimates of DOC and DOP bioavailability reduces estimates of elemental imbalance experienced by aquatic bacteria.</p

Data_Sheet_3_Bioavailability of Dissolved Organic Phosphorus in Temperate Lakes.DOCX

<p>Freshwater aquatic systems are biogeochemical hotspots, with heterotrophic bacteria rapidly cycling the compounds that pass through them. P is a key nutrient that controls primary production in many freshwater ecosystems and is important for understanding eutrophication in lakes. Previous work has often focused on the dynamics of inorganic phosphorus and its impact on primary production, however, the role of nutrients bound in more complex organic forms (such as dissolved organic phosphorus, DOP) in supporting primary production and harmful algal blooms has been neglected. Here, we quantify the bioavailability of dissolved organic carbon (DOC) and DOP in 27 aquatic systems across the Upper Midwest United States. Using exponential decay models, long-term nutrient degradation assays revealed that decay constants for DOP ranged from −0.001 per day to −0.12 per day with a median value of −0.01 per day. These rates were geographically variable and were as high or higher than DOC decay constants, which ranged from −0.003 per day to −0.024 per day with a median value of −0.01 per day. Additionally, total bioavailability of DOP ranged from 0 to 100% with a median value of 78% of the DOP pool, demonstrating that DOP bioavailability was highly variable across systems. In contrast, bioavailable DOC was more tightly constrained with values ranging from 4.37 to 53.81% of the total DOC pool with a median value of 24.95%. DOP bioavailability was negatively correlated with the DOC:DOP of the organic matter pool, suggesting that bioavailable DOP is drawn down in systems that are more likely to be P limited. Finally, we show that including estimates of DOC and DOP bioavailability reduces estimates of elemental imbalance experienced by aquatic bacteria.</p

Spatial and Temporal Distribution of Singlet Oxygen in Lake Superior

A multiyear field study was undertaken on Lake Superior to investigate singlet oxygen (¹O₂) photoproduction. Specifically, trends within the lake were examined, along with an assessment of whether correlations existed between chromophoric dissolved organic matter (CDOM) characteristics and ¹O₂ production rates and quantum yields. Quantum yield values were determined and used to estimate noontime surface ¹O₂ steady-state concentrations ([¹O₂]_ss). Samples were subdivided into three categories based on their absorbance properties (<i>a</i>300): <i>riverine</i>, <i>river</i>-<i>impacted</i>, or <i>open lake</i> sites. Using calculated surface [¹O₂]_ss, photochemical half-lives under continuous summer sunlight were calculated for cimetidine, a pharmaceutical whose reaction with ¹O₂ has been established, to be on the order of hours, days, and a week for the <i>riverine</i>, <i>river-impacted</i>, and <i>open lake</i> waters, respectively. Of the CDOM properties investigated, it was found that dissolved organic carbon (DOC) and <i>a</i>300 were the best parameters for predicting production rates of [¹O₂]_ss. For example, given the correlations found, one could predict [¹O₂]_ss within a factor of 4 using <i>a</i>300 alone. Changes in the quantum efficiency of ¹O₂ production upon dilution of river water samples with lake water samples demonstrated that the CDOM found in the open lake is not simply diluted riverine organic matter. The <i>open lake</i> pool was characterized by low absorption coefficient, low fluorescence, and low DOC, but more highly efficient ¹O₂ production and predominates the Lake Superior system spatially. This study establishes that parameters that reflect the quantity of CDOM (e.g., <i>a</i>300 and DOC) correlate with ¹O₂ production rates, while parameters that characterize the absorbance spectrum (e.g., spectral slope coefficient and E2:E3) correlate with ¹O₂ production quantum yields

Spatial and Temporal Distribution of Singlet Oxygen in Lake Superior

A multiyear field study was undertaken on Lake Superior to investigate singlet oxygen (¹O₂) photoproduction. Specifically, trends within the lake were examined, along with an assessment of whether correlations existed between chromophoric dissolved organic matter (CDOM) characteristics and ¹O₂ production rates and quantum yields. Quantum yield values were determined and used to estimate noontime surface ¹O₂ steady-state concentrations ([¹O₂]_ss). Samples were subdivided into three categories based on their absorbance properties (<i>a</i>300): <i>riverine</i>, <i>river</i>-<i>impacted</i>, or <i>open lake</i> sites. Using calculated surface [¹O₂]_ss, photochemical half-lives under continuous summer sunlight were calculated for cimetidine, a pharmaceutical whose reaction with ¹O₂ has been established, to be on the order of hours, days, and a week for the <i>riverine</i>, <i>river-impacted</i>, and <i>open lake</i> waters, respectively. Of the CDOM properties investigated, it was found that dissolved organic carbon (DOC) and <i>a</i>300 were the best parameters for predicting production rates of [¹O₂]_ss. For example, given the correlations found, one could predict [¹O₂]_ss within a factor of 4 using <i>a</i>300 alone. Changes in the quantum efficiency of ¹O₂ production upon dilution of river water samples with lake water samples demonstrated that the CDOM found in the open lake is not simply diluted riverine organic matter. The <i>open lake</i> pool was characterized by low absorption coefficient, low fluorescence, and low DOC, but more highly efficient ¹O₂ production and predominates the Lake Superior system spatially. This study establishes that parameters that reflect the quantity of CDOM (e.g., <i>a</i>300 and DOC) correlate with ¹O₂ production rates, while parameters that characterize the absorbance spectrum (e.g., spectral slope coefficient and E2:E3) correlate with ¹O₂ production quantum yields

6-Cinaruco Meiofauna Density Sand Exp

samples and calculations for meiofauna taxa and their densities in sand during fish exclosure/enclosure experiment

4-Cinaruco CHLA Sand Exp

samples and calculations for chlorophyll a accumulations in sand during fish exclosure/enclosure experiment

1-Cinaruco AFDM Tiles Exp

samples and calculations for particulate organic matter accumulations on tiles during fish exclosure/enclosure experiment

2-Cinaruco CHLA Tiles Exp

samples and calculations for chlorophyll a accumulations on tiles during fish exclosure/enclosure experiment

Appendix I. Natural seasonal variation of meiofauna density within sand from littoral zones of the river channel and floodplain lagoons.

Natural seasonal variation of meiofauna density within sand from littoral zones of the river channel and floodplain lagoons

5-Cinaruco Algal Biovolume Tiles Exp

samples and calculations for alga taxa and their biovolumes accumulations on tiles during fish exclosure/enclosure experiment