QUANTIFYING THE RELATIONSHIPS BETWEEN LAKE NUTRIENTS AND AGRICULTURAL LAND USE/COVER AT DIFFERENT SPATIAL SCALESByKatie L. DroschaI quantified agricultural land use/cover using five spatial metrics to determine which spatial metric was most strongly correlated with seasonal lake total phosphorus and total nitrogen concentrations in 204 Michigan lakes. I used two distance based spatial metrics, two flow direction spatial metrics and full lake catchments. Agricultural land use/cover was categorized as pasture, forage, row crop and total agriculture. My research questions were 1) which agricultural type and spatial metric is the most strongly correlated with lake nutrient concentrations, 2) How similar are the spatial metrics that quantify agricultural land use/cover in lake catchments, 3) Do the different spatial metrics each contribute to explaining lake nutrients, 4) Do different agricultural types have similar effects on lake nutrients. I used correlation coefficients to quantify the relationship between agricultural types, spatial metrics and seasonal lake TP and TN. Among agricultural types, the catchment, moderate-highly contributing area and 100 m lake-stream buffer spatial metrics were strongly correlated with each other, meaning they measured similar aspects of the landscape. Row crop and total agriculture had the strongest correlations for spring and summer lake nutrients, however, linear regression analysis within the 100 m lake-stream buffer reveal that for a change in one unit of pasture or forage, there is a larger change in lake nutrients when compared to row crop and total agriculture. Further research is needed to more fully quantify the effects of pasture and forage lands on lake nutrients.
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