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Long-term decreases in phosphorus and suspended solids, but not nitrogen, in six upper Mississippi River tributaries, 1991-2014.

Authors
  • Kreiling, Rebecca M1
  • Houser, Jeffrey N2
  • 1 US Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, WI, 54603, USA. [email protected]
  • 2 US Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, WI, 54603, USA.
Type
Published Article
Journal
Environmental Monitoring and Assessment
Publisher
Springer-Verlag
Publication Date
August 2016
Volume
188
Issue
8
Pages
454–454
Identifiers
DOI: 10.1007/s10661-016-5464-3
PMID: 27393194
Source
Medline
Keywords
License
Unknown

Abstract

Long-term trends in tributaries provide valuable information about temporal changes in inputs of nutrients and sediments to large rivers. Data collected from 1991 to 2014 were used to investigate trends in total nitrogen (TN), total phosphorus (TP), nitrate (NO3-N), soluble-reactive P (SRP), and total suspended solids (TSS) in the following six tributaries of the upper Mississippi River: Cannon (CaR; Minnesota (MN)), Maquoketa (MR; Iowa (IA)), Wapsipinicon (WR; IA), Cuivre (CuR; Missouri (MO)), Chippewa (ChR; Wisconsin (WI)), and Black (BR; WI) rivers. Weighted regression on time discharge and season was used to statistically remove effects of random variation in discharge from estimated trends in flow-normalized concentrations and flux. Concentration and flux of TSS declined in all six rivers. Concentration of P declined in four of the rivers, and P flux declined in five rivers. Concentration and flux of N exhibited small changes relative to TP. TN concentration and flux did not change substantially in four of the rivers and decreased in two (ChR, CuR). Nitrate concentration and flux increased in three rivers (ChR, BR, CaR) and remained relatively constant in the other three rivers. General declines in P and TSS suggest that improvements in agricultural land management, such as the adoption of conservation tillage and enrollment of vulnerable acreage into the Conservation Reserve Program, may have reduced surface runoff; similar reductions in N were not observed.

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