Biogeochemistry of Wet Ecosystems from Root Zone to Landscape
Kissoon, La Toya Tricia
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The biogeochemistry of wetland ecosystems varies, causing them to act as sources, sinks, filters or transformers of nutrients and pollutants. Wetland plants play important roles in the cycling of elements in wet ecosystems. The structural and physiological adaptations that allow these plants to colonize wetland habitats as emergent or submerged species contribute to biogeochemical processes in wetland substrates. Rhizosphere (root zone) oxidation, iron and manganese oxide precipitation, acidification of the rhizosphere, root exudation, and microbial activity influence the mobility of elements in wetland substrates. Both emergent and submerged wetland plants can alter conditions in the rhizosphere that influence the mobility of elements. These plants are also capable of removing elements such as Cd, Cu, Fe, Mn, N, P and Zn from solution and accumulating them in their tissues. Root zone studies were carried out in the greenhouse using the wetland plants Typha angustifolia (cattail) and Rumex crispus (curly dock) and in the field using Triglochin maritima (seaside arrowgrass) to determine differences in element concentrations in the root and bulk zone under different soil moisture conditions. Studies involving shallow lakes of Minnesota were carried out to determine relationships among (1) landscape variables (e.g. lake watershed size, percent agriculture, percent woodland), water and sediment characteristics (turbidity, chlorophyll-a, organic content, particle size), (3) element concentrations in waters and sediments, and (3) plant abundance and community composition. The studies reported here showed that different factors influenced the distribution of multiple elements in the root zone of emergent wetland plants and in waters and sediments of shallow lakes. First, the root zone studies indicated that pH, redox and moisture content of wetland soils influenced the distribution of elements in the rhizosphere and subsequent uptake of these elements by wetland plants. Second, the shallow lake study showed that land cover uses (agriculture and woodland), lake watershed size, and sediment physical characteristics (organic content and particle size) influenced the distribution of elements in waters and sediments of shallow lakes. Concentrations of these elements, land cover uses, open water area, turbidity, chlorophyll-a concentrations and sediment physical characteristics influenced abundance and distribution of submerged and floating plants.