Relationship of Benthic Productivity and Stream Water Chemistry:

The Influence of Landscape in Illinois Watersheds

S.E. Fanta, C.L. Pederson, and R.U. Fischer

Department of Biological Sciences Eastern Illinois University.

Introduction

With approximately sixty percent of Illinois’ total acreage consisting of cropland, it is vital to gain further understanding of effects that such vast amounts of agriculture have on the functioning of lotic systems. We hypothesize that changes in watershed landscape due to agriculture impacts the biota by changing the physical and chemical nature of streams.

Alteration of landscape leads to variation in aquatic ecosystems:
	Figure 1.  A quality ecosystem characterized by an extensive vegetated riparian zone. Streams such as this one shown here likely support a more diverse biota, perhaps as a result of more moderate temperature regimes and reduced input of nutrients and sediment from the surrounding terrestrial area.
	Figure 2.  Streams with watersheds altered through agricultural practices often are channelized and typically lack a vegetated riparian zone. Impacts on biotic processes often derive from excessive loading of sediments and nutrients as well as pronounced diurnal fluctuation in temperature.

Objective 1

Determine whether watershed land use/land cover and extent of stream riparian zones impact the physical and chemical characteristics of streams.

Sampling Regime

The study is being conducted over 1 calendar year (3 months remaining)

March to October (sampled every 2 weeks)

November to February (sampled every 4 weeks)

A total of 19 physical (e.g., temperature, stream depth) and chemical (e.g., phosphorus, nitrate, ammonia, dissolved oxygen) variables were measured at each of 12 sites in Hurricane Creek watershed.

	Figure 3.  Major Illinois river basins.
	Figure 4.  Embarras River basin showing the location of Hurricane Creek watershed.
	Figure 5.  Hurricane Creek watershed.

Results

Figure 6.

Principal Components Analysis (PCA) was used to combine measured variables into derived variables.  Analysis of variance (ANOVA) for PCA Factor 1 revealed significant differences among the 12 sites which were sampled (p < 0.001).  Twelve sites within the Hurricane Creek watershed can be grouped into 4 distinct "stream types" based on physical and chemical characteristics.

Figure 7.

Five sites with perennial instream flow were chosen for measurement of community metabolism.

Physical and chemical distinction of these stream types remained even when streams with more intermittent flows were eliminated from the analysis.  These five sites represented two of the "stream types" identified by PCA.  Sites 5, 11 and 12 are more heavily influenced by agriculture, typically with less than 15% of the riparian zone remaining as forest.  In contrast, Sites 6 and 9 are characterized by more intact riparian zones (ca. 30% forest or grassland).

Conclusion 1: The sites are different with respect to their physical and chemical nature. Most likely, stream types result from variation in land use/land cover and riparian zone vegetation.

Objective 2

Evaluate whether benthic algal productivity is influenced by the nature of the watershed.

Community Metabolism

Benthic algal productivity was determined at sites with perennial in-stream flow: Stream Type I (Sites 6 & 9) and Stream Type III (Sites 5, 11, & 12)  Each site was sampled in July and August, 2002 and March, 2003.  Using the dissolved oxygen method, we can determine levels of gross primary productivity and community respiration. The relative extent of oxygen production and consumption is measured and used to determine net daily metabolism. Photosynthetic activity by benthic algae during periods of daylight increases concentrations of dissolved oxygen in streams. Respiration by heterotrophic organisms will tend to decrease dissolved oxygen concentrations.

Figure 8.	Figure 9.
Field probes (Figure 8) and data logger (Figure 9) used to measure dissolved oxygen concentrations at 15 minute intervals over 24-hour period.

Figure 10.

Net Daily Metabolism is calculated as the difference between Gross Primary Productivity and Community Respiration. In this example, NDM = GPP – CR24: -10.44 mgO2 L-1 day-1 = 9.69 – 20.13

Conclusion 2

Negative values for net daily metabolism in July/August, 2002 suggest that the streams in Hurricane Creek Watershed are heterotrophic in late summer/early fall and therefore rely on allochthonous inputs from the watershed.  Additional determinations of community metabolism currently are being obtained to determine whether streams of the Hurricane Creek watershed are heterotrophic or autotrophic during late spring/early summer.  Knowledge of temporal and spatial variation in community metabolism is necessary for establishing the causative relationship of stream water chemistry and validation of our conceptual model.