Evaluating the effects of riparian habitat type on nutrient concentrations in agricultural headwater streams

Authors: BALCERZAK, A - The Ohio State University; Smiley, Peter - Rocky; KALCIC, MARGARET - The Ohio State University

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2022
Publication Date: 12/30/2022
Citation: Balcerzak, A.M., Smiley, P.C., Kalcic, M.M. 2022. Evaluating the effects of riparian habitat type on nutrient concentrations in agricultural headwater streams. Journal of the American Water Resources Association. 58(6):1497–1509. https://doi.org/10.1111/1752-1688.13052.
DOI: https://doi.org/10.1111/1752-1688.13052

Interpretive Summary: Grass filter strips and other riparian buffer types have been widely used within agricultural watersheds to improve water quality in agricultural streams. The understanding of the effectiveness of grass filter strips and other types of riparian buffers in reducing non-point source pollution is limited because most studies have focused on documenting the short-term plot scale effects and only a few have examined the long-term watershed scale effects. We measured nutrient concentrations from eight agricultural headwater streams in central Ohio for ten years and assessed if nutrient concentrations differed among streams with unplanted riparian habitats, streams with grass filter strips, and streams having forested riparian habitats. Nitrogen and phosphorus concentrations did not differ among riparian habitat types. Dissolved organic carbon concentrations differed among years in streams with herbaceous riparian habitat types (unplanted and grass filter strips), but did not differ among years in streams with forested riparian habitats. Additionally, dissolved organic carbon concentrations did not differ seasonally in streams with herbaceous riparian habitats, but differed seasonally in streams with forested riparian habitats. Our results represent the one of the few long-term watershed scale assessments of the influence of grass filter strips and existing forested riparian habitats on nutrient concentrations in agricultural headwater streams. Our results indicated that planting grass filter strips alone may not decrease nitrogen and phosphorus concentrations in agricultural headwater streams. Our results also highlighted the influence of riparian woody vegetation on the annual and seasonal changes of dissolved organic carbon concentrations, which is a nutrient that is important for stream ecosystem function. Our results will be of interest to state agencies, federal agencies, private consulting companies, and non-profits involved with the management of agricultural watersheds in the United States because they provide information that can assist with developing watershed conservation plans for agricultural headwater streams.

Technical Abstract: Grass filter strips and other riparian buffer types have been widely used within agricultural watersheds to address water quality issues. There is much information on the short-term plot scale effects of riparian buffers, but only a limited amount of information is available on their long-term watershed scale effects. Our research questions were: 1) does nutrient concentrations within agricultural headwater streams differ among streams having different riparian habitat types? and 2) does the effect of riparian habitat type differ annually or seasonally? Eight streams in a central Ohio watershed were selected based on watershed size, amount of agricultural land use in the watershed, and riparian habitat type. Three streams possessed unplanted riparian habitats with vegetation established through natural processes, three streams had grass filter strips planted along 40 to 50% of their respective stream lengths, and two streams had forested riparian habitats. Weekly water samples for the measurement of ammonium, nitrate + nitrite, total nitrogen, dissolved reactive phosphorus, total phosphorus, and dissolved organic carbon concentrations were collected from two sites in each stream from March 2007 to February 2017. Linear mixed effect model analyses indicated that mean nitrogen and phosphorus concentrations did not differ (P > 0.05) among riparian habitat types and that mean dissolved organic carbon concentrations exhibited different (P < 0.05) annual and seasonal trends among riparian habitat types. Our results indicated that planting grass filter strips alone may not result in large decreases in nitrogen and phosphorus concentrations and highlighted the influence of riparian woody vegetation on the temporal dynamics of dissolved organic carbon.