Epsilon Archive for Student Projects

Abstract

Eutrophication continues to be a persistent threat to the health of ecosystems globally and in the Baltic Sea region, causing a loss in ecosystems and industry profits. Measures have been researched and implemented to stop the spread of excess nutrients from agricultural sources, but innovative, cost-effective nutrient mitigation strategies are still needed to reach water quality targets.
Redesigning traditional trapezoidal ditches has been researched to offer alternative, sustainable methods of inducing water purification and biological physiochemical activity nearby agricultural fields. The two-stage ditch is a design that increases water retention by adding a flood plain buffer. This design encourages nutrient and carbon processing, including denitrification, sedimentation of particulate phosphate and sorption of phosphate among other processes. But generally, the role of ditch vegetation, particularly macrophytes, in promoting these processes is not well understood. Therefore, to improve this understanding of the role of macrophytes in ditch remediation, relationships between macrophyte diversity and abundance and water quality in two-stage ditches were studied.
This study was conducted in nine agricultural catchments where environmental factors (stream nutrient content, soil type, stream flow, land use, etc.) were investigated to explain macrophyte abundance and diversity during the summer growing period. An Ecological Quality Ratio was determined for each site and related to macrophyte diversity and water chemistry through the historical trends in total nitrogen and total phosphorus concentrations in each ditch. Macrophyte species that were most abundant at each site were then sampled for their total nitrogen and total phosphorus content and compared with the measured nutrient loads in their respective two-stage ditches.
The results showed that macrophyte communities commonly associated with eutrophic and mesotrophic aquatic environments, such as agricultural ditches, can be used as indicators for stream ecological quality that complement water chemistry measurements. Prevalence of certain macrophytes varied depending on the environmental characteristics, such as: ditch location and soil type and texture, but were heavily influenced by nitrogen and phosphorus availability. The total nitrogen concentrations in June of 2022 strongly negatively correlated with the macrophyte diversity recorded at that same time. The species identified for their nutrient retention capacity were: Typha sp., Phragmites australis, Epilobium hirsutum, and Alisma plantago-aquatica. Analysis of the August stream sample nutrient uptake data implies that species abundance and biomass affect water quality by decreasing nutrient availability in the water column and in turn are affected by water quality. Thus, harvesting them prior to decay is suggested as a remediation practice with potential for sustainable nutrient recycling, especially in two-stage ditches.