Groundwater flow influences on the biomass and nutrient ratios of epibenthic algae in a north temperate seepage lake
Hagerthey, Scot E., and W. Charles Kerfoot
Limnol. Oceangr. 43:1227-1242

Groundwater flow influenced epibenthic algal biomass and N: P ratios at a seepage lake (Sparkling Lake, Wisconsin). During seasonal studies, biomass and seepage flux were positively associated (r = 0.453; P < 0.001). Pore-water soluble reactive phosphorus (SRP) concentrations (29.2-110.7 µg PO, liter-‘), SRP fluxes, and algal biomass were significantly higher at high groundwater discharge sites than at low flow sites (< 10.0 to 27.7 µg PO4 liter^-l). Pore-water ammonia (NH₄⁺) concentrations were significantly lower at high groundwater discharge sites (<10.0 to 566.0 µg NH₄⁺ liter^-l) than at low groundwater discharge and recharge sites (61.4-1464.9 µg NH₄⁺ liter^-l). The coupling between pore-water nutrient concentrations and local groundwater flow dynamics suggests a mechanism for the observed spatial patterns in biomass. In situ experimental chambers evaluated coupling between epibenthic algal biomass, N: P ratios, and groundwater flow patterns. Biomass responded rapidly in chambers, reaching ambient levels within 1.5 months of initiation. Free-flow chambers in discharge regions had consistently higher soluble reactive phosphorus (SRP), NO₃-NO₂, and O₂ concentrations, higher phosphate and nitrate-nitrite fluxes, higher algal biomass, and lower N : P ratios in the developing mat. Free-flow chambers in recharge regions had high ammonia (NH₄⁺) concentrations, lower algal biomass, and higher N: P ratios. These results confirm that groundwater-related nutrient fluxes influence the local physicochemical environment and affect epibenthic algal biomass.