Concentrations and loads of nitrogen (N) and phosphorus (P), in both dissolved and particulate fractions, are sensitive to land cover and hydrologic variability. Previous studies on relationships between watershed characteristics and stream chemistry have focused on the response of individual N and P fractions. However, marine and lakes studies have shown the value of using individual nutrient fractions as well as nutrient ratios (e.g., N:P) to assess ecosystem condition. This study examined the response of total, dissolved, and particulate N and P fractions as well as N:P ratios to changes in % crop cover and hydrologic variability in three agricultural catchments in the Red River Basin, southern Manitoba, Canada. While discharge peaks were greatest during snowmelt for both study years (2013 and 2014), flow ceased in early June 2013 due to lack of precipitation whereas discharge peaks were observed during summer and fall 2014 in response to persistent multi-day rain events. Despite hydrologic differences between the two years, total, dissolved, and particulate N:P concentration ratios did not differ (p>0.05) between years (expressed as either annual or seasonal means) or in response to % crop cover. In contrast, N: P load ratios were associated with watershed characteristics: total N: P load ratios differed (p<0.05) in relation to both % crop cover and season, dissolved N:P load ratios differed (p<0.05) with % crop cover, and particulate N:P load ratios differed (p<0.05) between seasons and years. Our finding that dissolved versus particulate N:P load ratios responded differently to land use and hydrologic changes suggests the dissolved load ratios are more closely linked to land use activities whereas particulate loads ratios are largely influenced by interannual climate and discharge variability. Improved knowledge of the dominant nutrient forms and their transport pathways will assist in determining appropriate mitigation practices to reduce nutrient loads under a changing climate.
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I enjoyed reading the research paper and the presentation! Thank you for providing informative and valuable data on N:P stoichiometry and how dissolved and particulate fractions differ with land cover and hydrology.
I have a question in regards to the algal community in the study streams: Was sestonic or benthic algal communities collected for identification? If so, do you have an idea of what type of algae ( i.e. blue greens , green) exist in either low or high N:P values?
Thank you for your interest and question!
Yes, we did collect both sestonic and benthic phytoplankton samples. At the moment we have only measured Chlorophyll a (a rough estimate of phytoplankton abundance), and will be identifying phytoplankton communities in the near future.
If you are interested, there are several papers that can provide some insight of the phytoplankton communities in Lake Winnipeg, Manitoba, Canada:
1. H. J. Kling, S. B. Watson, G. K. McCullough & M. P. Stainton. 2011. Bloom development and phytoplankton succession in Lake Winnipeg: a comparison of historical records with recent data. Aquatic Ecosystem Health & Management Vol. 14 , Iss. 2,
2. McCullough, G.K., Page, S.J., Hesslein, R.H., Stainton, M.P., Kling, H.J., Salki, A.G. and Barber, D.G., 2012. Hydrological forcing of a recent trophic surge in Lake Winnipeg. Journal of Great Lakes Research, 38, pp.95-105
3. Schindler, D.W., Hecky, R.E. and McCullough, G.K., 2012. The rapid eutrophication of Lake Winnipeg: Greening under global change. Journal of Great Lakes Research, 38, pp.6-13