The influence of impoundments on nutrient budgets in two catchments of Southeastern Michigan |
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Authors: | Nathan S Bosch J David Allan |
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Institution: | (1) School of Natural Resources and Environment, University of Michigan, Dana Building, 440 Church Street, Ann Arbor, MI 48109-1041, USA |
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Abstract: | N and P budgets quantify inputs and outputs of nutrients at the catchment scale to allow evaluation of inputs and outputs
as well as inferences about transport and processing based on unaccounted-for nutrients. N and P budgets were constructed
for two catchments in southeastern Michigan with markedly different numbers of impoundments, over two years, to evaluate the
influence of impoundments on nutrient fluxes from each catchment. The Huron, with 88 impoundments >10 ha, stored 156 kg P km−2 y−1, while the Raisin (with 14 impoundments) had a net export of 102 kg P km−2 y−1. The Huron catchment also stored and denitrified more N than the Raisin catchment – 2,418 kg N km−2 y−1 compared to 1,538 kg N km−2 y−1. Riverine export of N and P also varied markedly between the catchments, with the Huron River exporting 288 kg N and 7 kg P km−2 y−1 and the Raisin River exporting 1,268 kg N and 34 kg P km−2 y−1. We then re-calculated budget results from previous studies using the approach of the present study, altering input and outputs
fluxes as well as system boundaries to obtain comparable budgets. For these comparable budgets, annual P outputs on average
accounted for 77% of inputs whereas N outputs accounted for only 39% of N inputs. Across catchments, the percent of inputs
exported by the river averaged 16% for N and 5% for P, indicating more effective retention of P than N. |
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Keywords: | Catchment Impoundments Mass balance Nitrogen Nitrogen budget Phosphorus Phosphorus budget Rivers |
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