Upper Midwest Environmental Sciences Center
Monitoring Activities and Highlights
Hydrology
Hydrologic analyses were performed on daily discharge data collected at
St. Paul, Minnesota; Keokuk, Iowa; and St. Louis, Missouri, for the Upper
Mississippi River, and at Kingston Mines, Illinois, for the Illinois River
(Table 1). Discharge values are calculated
from elevation gage readings via an elevation-discharge relation. The
period of record for the four stations ranged from 61 to 123 years. Watershed
areas for the four stations vary from about 2% to 99% of the total watershed
of the Upper Mississippi River, including the Missouri River watershed
(Table 1). Other information concerning the
discharge database are provided in a procedures manual (Wlosinski et
al. 1995).
Mean daily discharge (m3/sec) was calculated for each station from January 1 through September 30 for all years. Compared to historic means, total discharge for the first 9 months of 2000 was near normal at Keokuk, Iowa, but relatively dry at the other three stations (Table 1). Seasonally, discharge was low during the normal flood period of April and May, but above average in June and July (Figure 2).
Water quality monitoring within the LTRMP focused on variables that significantly affect aquatic habitats, including physicochemical features, suspended sediment, and major plant nutrients, in the Upper Mississippi River and its major tributaries. Sampling in 2000 followed the design that was established in 1993 as modified in 1999. The design combined quarterly episodes of stratified random sampling with sampling at fixed sites (mainly tributaries and major inflows and outflows) every 4 weeks. Stratified random sampling provides unbiased, seasonal information on water quality across broad areas, such as entire navigation pools. Fixed-site sampling provides more continuous information at specific locations.
The data collected by LTRMP show the broad influence of long-term climate variations and the interconnection among physical and chemical features of habitat in this system. For example, oxygen concentrations in winter vary with snow and ice cover (Figure 3). Because shading reduces photosynthesis (oxygen supply), oxygen concentrations are lower when ice and snow are thicker. The increase in winter oxygen concentration from 1996 to 2000 is slight (about 0.5 mg/L per year) but statistically significant (P < 0.001) as is the decline in snow and ice cover (about 5 cm per year, P < 0.001). Increased dissolved oxygen levels provide better winter habitat for fish and may help to increase fish survival over winter.
The status and trends of major plant nutrients, particularly nitrogen, and suspended sediment in the Mississippi River basin have been of national concern in recent years. The LTRMP monitors delivery of these materials to the river from their major sources. In 1999 and 2000, LTRMP monitoring was combined with USGS-funded research on the fate and effects of nitrogen within the river to provide a more complete picture of nitrogen dynamics and the potential for management of nitrogen inputs, transports, and effects. Results indicate that there is substantial capability to remove nitrogen as it moves downstream if nutrient rich water from the main channel can be moved into backwater areas.
The LTRMP data show notable patterns in nitrogen in the UMRS (Figures 4 and 5). In the upper pools, concentrations of nitrate plus nitrite appear to have stabilized after falling from highs observed during the 1993 flood (Figure 4). The reduced input of nitrogen from the upper portion of the basin during the low-flow summer of 1996 (Figure 4) is also evident. However, in Pool 26 and Open River Reach, nitrate concentrations have risen on average about 0.2 mg/L per year since the 1993 flood (Figure 5). This corresponds to a steady decline in river discharge during the same period.
Chlorophyll a concentrations (Figure 6) indicate
the abundance of suspended algae in the water, and although many factors
influence algal abundance, nutrients and light availability are usually
the most important. The elevated nutrient concentrations that occur in
the river have the potential to produce intense algal "blooms,"
but this is often prevented by low light penetration. For example, the
summer chlorophyll data from Pool 26 show that although nitrate concentrations
in the main channel were high in 1996 (Figure
5), mean algal abundance was low (Figure 6).
Suspended solids concentrations were also high in 1996 (median = 120 mg/L)
and thus light limitation appears to have been more important to algal
abundance than the stimulus provided by nutrients. However, the sharp
increase in algal variability in recent summers (Figure
6) suggests that when light limitation is relieved for short periods,
intense but intermittent algal blooms can develop.
The Upper Mississippi River System supports important recreational and commercial fisheries. Fish species and communities were monitored with standard procedures (Gutrueter et al. 1995; Burkhardt et al. 2000) in all six LTRMP study reaches (Figure 1). In 2000, fish were sampled at stratified random and fixed sampling locations with electrofishing, hoop nets, fyke nets, seines, and trawls. There was a reduction in effort of 116 samples in 2000, primarily in gears used in the offshore strata. This was a result of a "first round" refinement of gear allocation based on power analysis of the 1993-1999 fish data.
A total of 2,498 samples were collected within the six study areas in
2000, yielding 395,333 fish and 61–74 species per reach. Most catches
were similar to previous years although several state–listed threatened
and endangered species were collected including, in Pool 8, blue sucker
(Cycleptus elonatus), river redhorse (Moxostoma carinatum),
goldeye (Hiodon alosoides), and black buffalo (Ictiobus niger);
in Pool 13, grass pickerel (Esox americanus vermiculatus), bluntnose
darter (Etheostoma chlorosomum), western sand darter (Ammocrypta
clara), and pugnose minnow (Opsopoeodus emiliae); in Pool 26,
western sand darter; and in Open River Reach, blue sucker, paddlefish (Polyodon spathula), mooneye (Hiodon tergisus), Mississippi
silvery minnow (Hybognathus nuchalis), silver chub (Macrhybopsis storeriana),
and striped mullet (Mugil cephalus).
Three species of exotic Asian carps were collected in 2000: silver
(Hypothalmichthys molitrix), bighead (H. nobolis),
and grass carps (Ctenopharyngodon idella). All three species were
limited to the lower three study areas, but catches were substantially
higher in 2000 compared to 1999 (Figure 7).
Bighead carp, which were first collected in 1994, showed dramatic increases
in Pool 26 and La Grange Pool. The total catch at La Grange Pool
of 1,142 fish is an order of magnitude higher than any of our previous
catches. Silver carp, which first appeared in our catch in 1998, increased
greatly in Open River Reach and La Grange Pool. Both species may
be poised to continue their expansion upstream.
Data analyses conducted to investigate ways to refine the LTRMP fish sampling protocol were completed in September 2000. Recommendations from these analyses will be reviewed by the LTRMP partners and possibly implemented for the 2001 sampling season.
In 2000, in addition to our normal monitoring, we conducted sampling
to examine the similarity of selected measures of fish abundance and community
structure between the existing LTRMP study areas and adjacent river pools
or reaches. Sampling, mainly electrofishing, was conducted from June 15
to October 31 in Pools 3 and 5, 12 and 14, 19 and 20, and in two reaches
of the Open River upstream and downstream of the Open River Reach. Results
from this study will test the assumption that fisheries resources in UMRS
pools within the same geomorphic reach of river are similar and respond
similarly to annual environmental variability. Analyses of these data
will be conducted in 2001.
Submersed aquatic plants are an important component of the Upper Mississippi River ecosystem. They provide food for migratory waterfowl, improve water quality by stabilizing sediments and assimilating nutrients, provide spawning and nursery areas for fish, and support invertebrate populations by providing structure and surface area.
Sampling of submersed aquatic vegetation was conducted with two protocols
in 2000. The primary protocol, referred to as "stratified random
sampling" (Yin et al. 2000), has been used since 1998 to sample
aquatic vegetation in June and July. This protocol was used in all LTRMP
focal areas except for the Open River Reach because this reach has virtually
no submersed aquatic plants. Sampling points were confined to areas <2.5 m deep. Areas deeper than 2.5 m generally do not support aquatic vegetation
given the turbidity in the river; thus, they were considered nonvegetated
and not sampled. The second protocol, referred to as "transect sampling"
(Rogers and Owens 1995), has been used since 1991 to sample aquatic plants
in May and June and August and September in about 32 selected backwaters within
Pools 4, 8, 13, 26, and La Grange Pool. This was the last year that
transect sampling was used. Unless stated otherwise, results presented
here were from stratified random sampling.
In Pools 4, 8, and 13 during 2000, the percentage frequency of occurrence
of submersed aquatic plants ranged from 39 to 58 (Figure
8) with 15 to 16 species collected in each pool. The most abundant
species in Pools 4, 8, and 13 were coontail (Ceratophyllum demersum),
Canadian waterweed (Elodea canadensis), sago pondweed (Potamogeton
pectinatus), and wild celery (Vallisneria americana). In contrast,
in Pool 26, only 6% of samples contained vegetation (Figure
8) and six species were found, with sago pondweed and coontail being
most common. In La Grange Pool, no submersed vegetation was found
(Figure 8).
As in previous years, submersed aquatic vegetation was abundant upstream
of Dam 13, and sparse elsewhere in the Upper Mississippi River System.
The primary factors responsible for this longitudinal pattern are probably
turbidity, water level fluctuation patterns, and abundance of off-channel
water areas. However, within a single pool, it appears that water depth,
current velocity, and turbidity, especially due to wind fetch, are the
primary factors that determine distributional patterns and species heterogeneity.
Within pools, some local changes were observed in 2000. An increase in
submersed vegetation was recorded in the lower half of Lake Pepin (Pool
4) and in the isolated lakes behind levees at the mouth of the Illinois
River in Pool 26. In Pool 8, submersed vegetation decreased in contiguous
backwaters and the impounded area.
Macroinvertebrates, especially mayflies (Ephemeroptera), fingernail clams (Sphaeriidae), and midges (Chironomidae), are important foods for a variety of fish and waterfowl and are important ecologically for digesting organic material and recycling nutrients. In 2000, macroinvertebrate sampling was conducted at all six LTRMP study areas using our standard sampling procedures (Thiel and Sauer 1999). Quantitative sampling was conducted for mayflies, fingernail clams, midges, Asiatic clams (Corbicula sp.), and zebra mussels (Dreissena polymorpha). The presence or absence of Odonata, Plecoptera, Trichoptera, Diptera, Bivalvia, Oligochaeta, Decapoda, Amphipoda, and Gastropoda were also reported.
Poolwide density estimates for mayflies and fingernail clams were highest in Pool 8 (Figures 9 and 10). Mayfly densities increased in Pool 4, but were relatively stable in all other study areas. Within pools, the greatest densities of both mayflies and fingernail clams occurred in impounded areas or backwater contiguous areas. Midge densities increased in Pool 13 to the highest levels yet recorded, but dropped in Pool 4 (Figure 11). All other pools were relatively stable. In all study areas, midge densities were highest in backwater contiguous areas. Zebra mussel densities increased in Pools 8 and 26 and reached the highest levels yet recorded for both areas (Figure 12). In Pool 13, zebra mussel densities dropped and continued to exhibit large annual fluctuations seen since 1996. Within pools, zebra mussel densities were highest in main channel border areas or side channels. Over all locations, the silt clay and silt clay with sand substrates supported the highest mean numbers of mayflies, fingernail clams, and midges. Not surprisingly, the highest densities of zebra mussels were found on the gravel rock substrates. Oligochaeta (aquatic worms and leeches) were present in 68% of samples and were the only presence or absence taxa that were present more times than they were absent.
This summary provides a cursory view of the major highlights from the Long Term Resource Monitoring Program in 2000. For more detailed information, we highly recommend the reader review the individual annual reports for 2000 (fisheries, vegetation, and macroinvertebrates).
Page Last Modified: April 17, 2018