Effects of Land Use on the Diversity, Productivity, and Presence of Invasive Species in Aquatic Plant Communities

D.S. Mason
Department of Environmental Science, The Richard Stockton College of New
Jersey, Galloway, NJ 08205-9441 Email: 0davidmason@gmail.com

E.L. Parker
Department of Environmental Science, Towson University, Towson, MD 21252
Email: eparke11@students.towson.edu

Introduction

retrieving samples from the lake

Land use is changed from natural habitats to urban and agricultural areas with the development that accompanies a growing population. Developing forest into urban and agricultural land uses can affect freshwater stream ecosystems by changing the nutrient profile and volume of surface runoff. Increased surface runoff causes a reduction in base flow and episodic flooding events. The impact of these changes can be monitored by sampling aquatic vegetation because species within aquatic vegetation communities are variably suited to a constrained range of physical and chemical stream parameters. A change in these parameters will alter the aquatic vegetation community. The objective of this research was to qualify the relationship between urban, agricultural, and forest land use and productivity, diversity, and dominance of invasives in aquatic vegetation communities.

Sites and Methods

EPA hydrologic monitoring stations were used for 12 sites spread between three watersheds. The watersheds were characterized as minimally impacted (Flat Brook), mixed urban and agricultural (Wallkill), and urban (Rockaway). Percent vegetation cover and stream habitat parameters were recorded in the field. After species were identified using the USDA online plants database, percent dominance and biomass of species were determined. Species richness, species evenness, diversity, dominance of invasive species, and primary production were calculated. Land use /Land cover information from the NJDEP 2007 data set was applied to study these parameters in the Flat Brook, Wallkill, and Rockaway River watersheds (NJDEP, 2007). Land cover was delineated using the Level 1 Anderson Classification System and summarized by total acres within each watershed. Total acreage was used to compare the percentage of each land use across the watersheds. Annual mean flow and water quality data was collected from the USGS National Water Information System online repository.

aquatic vegetation sampling sites

Results

The most diverse stream was the Wallkill, followed by the Rockaway, then the Flat Brook. The Flat Brook had the lowest nutrient concentrations and species diversity of the three rivers sampled. The Wallkill had the highest nitrate and nitrite concentrations, as well as the greatest productivity, species diversity, and percent cover of invasive species. The Rockaway had intermediate levels of nitrite and nitrate as well as intermediate diversity and the lowest percent cover of invasive species. The two invasive species found were Myriophyllum spicatum (Eurasian watermilfoil) and Potamogeton crispus (curly pondweed). The productivity of Wallkill was twice that of Rockaway. Wallkill productivity increased moving downstream; results were inconclusive at the Rockaway and Flat Brook.

aquatic vegetation charts

Discussion

Nutrients and substrate limit productivity and diversity of aquatic plants in streams. The Flat Brook had the lowest biodiversity, the Rockaway had intermediate biodiversity and half the production of the Wallkill, and the Wallkill had the greatest productivity and biodiversity of all three streams sampled. The high percentage of forest and wetlands in the Flat Brook watershed reduce erosion, limiting nutrient run off and siltation. The mid-range levels of productivity and diversity seen at Rockaway sites can be explained by the high percentage of urban land use because impervious surfaces increase runoff and siltation. The concept is supported by the relatively high production and diversity levels seen at the Wallkill sites. In addition to the siltation effects of urbanization, agriculture in the Wallkill watershed contributed to more siltation and higher nutrient concentrations. This high level of nutrients and siltation
provided the best habitat for aquatic vegetation communities, The greater percent cover of invasive species within the Wallkill as compared to the other streams could be explained by the fact that invasive species respond favorably to the same conditions as native species (Caspers et al., 2003). If habitat
integrity is incumbent upon maintaining communities of native species, changing land use is detrimental because it increases suitable habitat and allows invasive species to infiltrate the ecosystem.

Literature Cited

  1. Capers, R. S., Selsky, R., Bugbee, G. J., White, J. C. (2007). Aquatic plant community invasibility and scale- dependent patterns in native and invasive species richness. Ecology, 88(12), 3135-3143. Retrieved from http://www.esajournals.org/loi/ecol/
  2. New Jersey Department of Environmental Protection (NJDEP), Office of Information Resources Management (OIRM), Bureau of Geographic Information Systems (BGIS). NJDEP Land use / Land Cover Update, 2007. (Vector Digital Data). Trenton, NJ.

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