Watershed Buffering of Anthropogenic Phosphorus Pressure PDF Download

Author: Anna Kusmer
Publisher:
ISBN:
Category :
Languages : en
Pages :

Get Book

Book Description
"Phosphorus (P) is a non-renewable resource that is an essential element for agricultural crop production. However, when excess P enters fresh and coastal water systems, it can result in undesirable impacts such as the excessive growth of algae species and oxygen depletion. Millions of tonnes of P are applied to agricultural lands every year in the form of phosphate fertilizer to increase yields. While some of this P is taken up by crops, much is left on the land, and this P has a tendency to stay in the soil, which results in a build-up of P in agricultural landscapes that can last years or even centuries. This build-up of historic P inputs, also known as "legacy P", represents a threat to surrounding water bodies because erosion and runoff processes can transport P-enriched soils to water systems.The processes that transport P from upland soils to water bodies are varied depending on the biological and biophysical features of the landscape as well as the human management features of the landscape. Together, these features mediate the residence time of P in the soils and landscape. The ability of a watershed to retain historic P inputs is its "buffering capacity", its ability to buffer the water quality from the impact of current and historic P inputs to the watershed. In this thesis, I ask, "how does buffering capacity vary among watersheds in southern Quebec over a thirty-year period of intensive farming?" and "which watershed characteristics impact watersheds' buffering capacity and the transport of legacy P from land to water systems?"I used two different methods to determine the buffering capacity of watersheds. One method compares the long-term P accumulation of a watershed to current day riverine P flux values. I call this the Buffering Index (BI). The other method, known as Extended End-Member Mixing Analysis (E-EMMA) uses hydrological modeling to estimate the degree to which P is retained and released by watershed ecosystems as water moves through the landscape. These two values were calculated for sixteen different watersheds in the Saint Lawrence Basin, in Quebec, Canada, spanning a thirty-year period (1981-2011). I then compared these values to geochemical, hydrological, landscape, and socio-ecological factors to determine which factors are important in predicting buffering capacity. All of the study watersheds have been accumulating P in their soils throughout the study period. My comparison of average riverine P flux values with average NAPI values showed that the study watersheds retained, on average, between 58% and 97% of net imported P in a given year. In general, watersheds with more P accumulation have higher riverine P flux; however, in many watersheds, riverine P flux has decreased over the study period, despite the fact that the amount of P accumulation in the watersheds has continued to mount over this time. I found a range of BI and E-EMMA values among the watersheds, along with a range of geochemical, hydrological, landscape, and socio-ecological characteristics. There was no correlation between the two buffering metrics calculated for the watersheds suggesting that these two metrics measure different buffering phenomena. However, each of the buffering indicators correlate with various watershed characteristics. This suggests that geochemistry, hydrology, and landscape features may, indeed, play a role in determining various aspects of the overall buffering capacity of watersheds. Determining which landscape features impact agricultural landscape buffering capacity can help us to understand how landscapes can be managed to increase their resilience to external pressure and identify leverage points for more holistic land management. A greater understanding of how buffering capacity is conferred on a watershed can also help identify which watersheds are particularly vulnerable to P pressure that could arise from changes in land use, including agricultural intensification and urbanization. " --