Susan P. Hendricks

Temperature patterns within the hyporheic zone of a northern Michigan river

Streambed temperature patterns were measured in three riffles of a northern Michigan (USA) warmwater river using 95-cm long stainless steel temperature probes. In riffles with uniform small particle substrata, patterns suggested that streamwater infiltration occurred at the head of riffles, affecting substrate temperatures as much as 50 cm deep. At the downstream end of riffles, cool water was much nearer the streambed surface. Temperature patterns were very irregular when large rocks occurred in and on the bed. These data also suggest that streambed temperature patterns may be a useful tool in determining the presence and extent of hyporheic zones and in determining longitudinal and physical stream characteristics likely to indicate where hyporheic zones exist.

Microbial Ecology of the Hyporheic Zone: A Perspective Integrating Hydrology and Biology

A case study of hyporheic research in a northern Michigan river is presented to illustrate some potential effects of subsurface hydrology on microbial ecology. Hydrologic flow between a downwelling and an upwelling zone beneath a riffle-pool sequence promoted hyporheic-groundwater interaction and differentiated regions of increased bacterial activity, production, turnover time, and responsiveness to dissolved organic carbon enrichment. Large gaps in knowledge exist on the structure and function of fungal, bacterial, microalgal, protozoan, and micrometazoan assemblages within hyporheic zones. This study, combined with available literature on surface and groundwater microbial assemblages, generated several hypotheses for future research. Hydrological methods, when coupled with biochemical measurements, micro-techniques, and descriptions of hyporheic physicochemical and biological gradients, can potentially contribute to a greater understanding of the role of hyporheic microbial communities in the structure and function of lotic ecosystems.

Relationships between hydraulic parameters in a small stream under varying flow and seasonal conditions

Twenty conservative tracer injections were carried out in the same reach of a small woodland stream in order to determine how variation in discharge and leaf accumulation affect stream hydraulic parameters. The injections were made at various discharge rates ranging from 2·6 to 40 l/s. Five of the injections were made during late autumn, when there were large accumulations of leaves in the stream. Estimates of hydraulic parameters were made by fitting a transient storage solute transport model to conservative tracer concentration profiles. Velocity increased almost linearly with increasing discharge, indicating a decline in the Darcy friction factor. Dispersion also increased with increasing discharge, especially for the lower flow injections. The relative size of the storage zone was small (∽0·1). There was no definable relationship between discharge and the relative storage zone size, but the rates of exchange between the storage zone and the main channel increased markedly with increasing discharge. The presence of large accumulations of leaves had a clear effect on the hydraulic characteristics of the stream, producing much higher friction factors, larger storage zone sizes and lower velocity than would have been predicted by discharge alone. Copyright

Longitudinal Patterns of Nutrient Cycling and Periphyton Characteristics in Streams: A Test of Upstream-Downstream Linkage

We studied trends in nutrient cycling and periphyton characteristics (biomass, species composition, productivity, and nutrient content) along longitudinal gradients in laboratory streams to test the hypothesis that upstream-downstream linkages produce distinct longitudinal patterns in stream ecosystems. Periphyton communities were grown under uniform light and flow conditions in two 88-m-long laboratory streams created by connecting four channel segments (each 0.3 m wide and 22 m long) in series. At the end of 8 wk, large longitudinal declines in streamwater N and P concentrations were observed in each stream. Although chlorophyll a declined and the proportion of cyanobacteria in the periphyton increased with distance downstream, longitudinal trends in ash-free dry mass, gross primary productivity (GPP), and total respiration were not significant. In contrast, longitudinal trends in most of the parameters related to nutrient deficiency and cycling were significant. Chlorophyll-specific phosphatase activity and C: nutrient ratios in periphyton biomass increased from upstream to downstream, suggesting greater nutrient deficiency downstream. Ratios of net N uptake rate: GPP and net P uptake rate: GPP declined from upstream to downstream, suggesting that nutrient recycling supported a greater fraction of the algal nutrient demand downstream. Ratios of net: total P uptake rate also declined from upstream to downstream, suggesting that a larger fraction of the total P uptake from stream water downstream was met by P recycled within the segment rather than by inputs from upstream. Within-segment recycling supplied only 10-25% of P uptake from stream water in upstream segments but contributed 60-70% of the P uptake from stream water in downstream segments. Finally, total P uptake rate: GPP ratio declined from upstream to downstream, suggesting that cycling of P within the periphyton mat was greater downstream than upstream. Together, our results showed that increased nutrient cycling can compensate for longitudinal declines in nutrient concentrations in stream water, preventing large longitudinal changes in periphyton biomass and productivity. Nutrient cycling and algal species composition were the characteristics showing strongest longitudinal linkage in these periphyton-dominated streams, whereas total biomass and productivity patterns were poorly related to longitudinal position.

Factors regulating autotrophy and heterotrophy in the main channel and an embayment of a large river impoundment

We characterized seasonal patterns of phytoplankton and bacterial biomass, production and nutrient limitation along a lateral transect within a large river impoundment. We hypothesized that the balance between autotrophy and heterotrophy was related to depth gradients and differences in water residence time (WRT) between the main channel and an embayment. Heterotrophy predominated in the main channel with bacterial production exceeding phytoplankton production by a factor of 3.3. In the embayment, autotrophy and heterotrophy were more closely balanced (ratios of bacterial to phytoplankton production ca. 0.8). Phytoplankton and bacterial biomass were positively correlated with WRT. However, WRT accounted for less than 50% of variation and its predictive power was comparable to models based on nutrient or DOC concentrations. Bacterial production was correlated with phytoplankton biomass and production suggesting that algal-derived C may be an important substrate for bacterial growth even in systems dominated by allochthonous inputs. Our experimental data suggest that nutrient limitation may be important particularly in embayments where biomass was somewhat higher and substrate concentrations were lower. Nutrient limitation in the main channel was rare whereas N and P amendments consistently stimulated phytoplankton growth rates in the embayment. Bacterial cell densities did not respond to nitrogen or phosphorus additions in either the main channel or embayment.

Nutrient Patterns in a Mainstem Reservoir, Kentucky Lake, USA, Over a 10-year Period

ABSTRACT Nutrient patterns were examined spatially and temporally from 1989 to 1998 in Kentucky Lake U.S.A., the largest mainstem reservoir on the Tennessee River system. Nutrients included NO3 −-N, NH4 +-N, PO4 −, SiO2, SO4 −2, and Cl−. Seasonal patterns in most nutrient concentrations were described well by cosine functions. Seasonal descriptions had less variance than discharge related descriptions of nutrient concentrations, possibly due to regulation of reservoir discharge. Differing land-use practices on either side of the reservoir were associated with significantly different nutrient concentrations in their related embayments. The agriculturally dominated western side embayments had lower nutrient concentrations than either the forested eastern side of the reservoir or mainstem sites. Annual average nutrient concentrations did not vary greatly over the 10-year period, indicating no change in eutrophication potential during the sampling period. An exception was a significant decline in SO4 −2 levels from 23 mg·L−1 in 1992 to 12.8 mg·L−1 in 1998. Annual export of nutrients was computed from yearly regressions on seasonal concentrations and daily discharge rates.

Benthic Diatom Species List and Environmental Conditions in the Little River Basin, Western Kentucky, USA

ABSTRACT Two hundred eighty-two taxa of diatoms (Bacillariophyta) were identified from composited benthic samples collected at 16 sites on the Little River in western Kentucky in 2000 and 2003. The Little River basin is heavily impacted by non-point source pollution consisting of high nutrient inputs and siltation from agricultural and urban runoff. Pennate diatoms dominated the flora comprising >96% of the total taxa throughout the basin. Commonly occurring pennate species included Achnanthidium minutissimum, Amphora perpusilla, Cocconeis placentula var. euglypta, Gomphonema parvulum, Navicula cryptocephala, N. cryptotenella, N. menisculus, N. minima, N. seminulum, N. tripunctata, Nitzschia amphibia, N. dissipata, N. frustulum, N. palea, Planothidium lanceolata, and Sellophora seminulum. Most common centric species were Cyclotella meneghiniana and Melosira varians. The number of taxa found in the Little River was similar to other eastern North American streams and typical of streams impacted by agricultural and urban non-point source pollution (organic and nutrient enrichment and high siltation). A species checklist of all diatom taxa identified in the Little River with currently accepted nomenclature is presented as a baseline for future comparisons.

Groundwater Flow and Reservoir Management in a Tributary Watershed along Kentucky Lake

ABSTRACT Understanding groundwater flow in tributary watersheds is important for evaluating water and solute storage and inputs into reservoirs. We delineated groundwater flow at various spatial and temporal scales within the watershed of Ledbetter Creek, a third-order tributary of the Tennessee River (impounded to create Kentucky Lake) in western Kentucky. We monitored hydraulic heads in wells (primarily in the upper watershed) and piezometers (in the lower watershed) and measured the flow of a spring along the embayment where the creek enters the reservoir. Manual measurements were made at least quarterly from July 1999 to March 2002 and were made annually each April from 2002 through 2006. From May 2000 to March 2002, hydraulic heads were recorded continuously in selected piezometers. At the watershed scale, groundwater flow followed the topography, with discharge occurring along the creek and in the embayment. Hydraulic heads in piezometers responded to large storms over periods of hours to days. Longer-term fluctuations in hydraulic head reflect reservoir management in the embayment (stage increased in early spring and decreased in late summer) and seasonal variability elsewhere in the watershed.

Incorporating a Watershed-Based Summary Field Exercise into an Introductory Hydrogeology Course

We have developed and implemented a summary field exercise for an introductory hydrogeology course without a laboratory section. This exercise builds on lectures and problem sets that use pre-existing field data. During one day in April, students measure hydraulic heads, stream and spring flow, and stream-bed seepage within the rural watershed of a third-order perennial stream in western Kentucky. Students calculate net specific discharge at various scales, map groundwater flow in the watershed, and calculate vertical hydraulic gradients at the mouth of the watershed, where the stream enters a reservoir (Kentucky Lake). Distinctive features of the exercise include hydraulic head measurements in large-diameter domestic wells and in piezometers installed in the reservoir embayment. Kentucky Lake is raised ~ 2 m shortly before the field trip, thus providing an analog of bank storage. Former students who responded to a questionnaire indicated that the exercise was worthwhile. The exercise was based at a biological field station but could be completed at any field site where long-term hydrologic monitoring is in place or could be initiated.

Benthic Algae Taxa (Exclusive of Diatoms) of the Little River Basin, Western Kentucky, 2000–2003

ABSTRACT The Little River is a highly disturbed system, heavily impacted by non-point source pollution from agricultural runoff in the form of excessive siltation, nitrogen and phosphorus, and organic pollution. Sixty-seven taxa of non-diatom benthic algae were documented for 16 sites in the Little River basin of western Kentucky during four sampling periods in 2000 and 2003. Algal taxa most often encountered included members of the Cyanophyta: Oscillatoria lutea (15 of 16 sites), O. subbrevis (13 of 16 sites), and Schizothrix calcicola (15 of 16 sites). Chlorophyta taxa most often encountered included Oedogonium sp. and Rhizoclonium hieroglyphicum, both at 10 of 16 sites. No trends were found between the algal taxa and areas of nutrient enrichment in the Little River basin. Because little is known of the benthic algal flora in the Little River, this report represents information complementary to that published previously on the benthic diatom taxa found at the same sites during the same study period.