Matthew F. Knowlton

Flooding to Restore Connectivity of Regulated, Large-River Wetlands Natural and controlled flooding as complementary processes along the lower Missouri River

You can always count on finding the Mississippi just where you left it last year. But the Missouri is a tawny, restless, brawling flood. It cuts corners, runs around at night, fills itself with snags and traveling sandbars, lunches on levees, and swallows islands and small villages for dessert. Its perpetual dissatisfaction with its bed is the greatest peculiarity of the Missouri.... It makes farming as fascinating as gambling. You never know whether you are going to harvest corn or catfish (Fitch 1907, p. 637).

Limnology Of Missouri Reservoirs: An Analysis of Regional Patterns

ABSTRACT Data from 94 Missouri reservoirs demonstrated a large interregional variation in total phosphorus (TP), total nitrogen (TN), algal chlorophyll (Chl), and suspended solids among the four physiographic provinces with numerous reservoirs. The interprovincial pattern for nutrients, algal biomass, and mineral turbidity was Ozark Highlands < Ozark Border ≃ Glacial Plains < Osage Plains corresponding to an interregional gradient between forest and agriculture as the dominant land cover. On the basis of TP most Missouri reservoirs were eutrophic (61%) or mesotrophic (21%) with few hypereutrophic (7%) or oligotrophic (11%). Statewide, water clarity was low (median Secchi depth 1.0 m) and more strongly related to non-volatile suspended solids (NVSS, R2 = 0.80) than algal Chl (R2 = 0.30). Summer mean values showed a curvilinear relation between Chl and TP (log10 transformed) reaching an asymptote above ≃ 50 μg/L TP/L — a range where most reservoirs have high NVSS and low TN:TP. Nitrogen limitation, light li...

Trophic status of Missouri River floodplanin lakes in relation to basin type and connectivity

Limnological data were collected over a two-year period from 12 lakes in the Missouri River floodplain in order to evaluate lake trophic status and the influence of basin type and connectivity on nutrient, seston, and phytoplankton dynamics. The lakes were located in west-central Missouri and included eight scour basins formed by levee breaks during a 1993 flood and four older oxbow lakes. The Missouri River was also sampled. Five of the scour basins (connected scours) were inundated by the Missouri River for varying periods during the study. The other lakes (protected lakes) were hydrologically isolated from the river by levees. On the basis of mean total phosphorus (TP-61-282 μg/L), mean total nitrogen (TN-0.7-2.1 mg/L), mean chlorophyll (CHL-22-67 μg/L), and mean suspended solids (TSS-16-93 mg/L), all 12 sites were highly eutrophic compared to other lakes in Missouri. Nutrient fractions and seston composition indicated dominance of inorganic nutrients and abiotic seston in the riverine lakes. Maximum concentrations of nutrients and TSS occurred in oxbow lakes during periods of sediment resuspension and in connected scours during floods in spring 1995 and 1996 when connected sites were inundated by the Missouri River. Algal blooms with peak CHL>200 μg/L occurred sporadically in the oxbow lakes. Similarly large blooms (peak CHL 81–689 μg/L) occurred in connected scours when low river levels reduced exchange with the river. Reduced connectivity was accompanied by rapid loss of dissolved N and P fractions, especially nitrate. Protected scours had lower average TP, TN, and TSS than the other sites and were less temporally variable.

Nutrients, seston, and transparency of Missouri reservoirs and oxbow lakes: An analysis of regional limnology

Abstract A long-term (1978–2007) summer monitoring study of 167 Missouri reservoirs and floodplain lakes shows wide ranges in the trophic state variables total phosphorus (TP; 6–395 μg/L for reservoir means), total nitrogen (TN; 200–3290 μg/L), chlorophyll (Chl; 1–223 μg/L) and Secchi depth (0.15–4.3 m). There are strong regional contrasts between eutrophic-hypereutrophic water bodies in the predominantly agricultural Osage Plains, Glaciated Plains and Big Rivers sections and the mostly oligotrophic-mesotrophic reservoirs in the largely forested Ozark Highlands. The ecotonal Ozark Border was intermediate. Missouri reservoirs had slightly less TN relative to TP than predicted by global models, but TN:TP (median = 18.4) is typical of North American lakes and was about five- fold lower in the most enriched reservoirs compared to the least enriched ones. Concentrations of seston, measured as total suspended solids (TSS), volatile suspended solids (VSS), nonvolatile suspended solids (NVSS), filterable (small) suspended solids (fTSS) and the sum of all fractions (ΣTSS), were strongly correlated with TP, TN, and Secchi depth. The proportion of mineral seston (NVSS, fTSS) increased with TSS and was the dominant fraction in most reservoirs, especially in the agricultural regions. Phytoplankton was dominated by small forms (<11 μm), and Cyanophyta were the most common algae comprising a median 46% of phytoplankton biovolume. Chlorophyll-nutrient regressions showed a dominant effect of TP (r2 = 0.83 for reservoir means) with a lesser, negative effect of mineral seston (NAS or fTSS, partial r2 ~ 0.05). Secchi depth was more strongly controlled by mineral seston than by phytoplankton such that Secchi was a better predictor of nutrients (especially TP) than algal biomass. Frequency of algal blooms (Chl >10 μg/L) and Secchi <1 m increased sigmoidally with TP and TN with midrange nutrient concentrations (TP 20–50 μg/L, TN 400–700 μg/L) showing the greatest response to change. Trophic state criteria appropriate for Missouri reservoirs are similar to other north temperate lakes except for Secchi depth for which cutpoints are much lower because of nonalgal turbidity.

Limnological reconnaissance of waterbodies in central and southern Nepal

Ionic composition of waterbodies in central and southern Nepal sampled in spring 1985 differed from that normally found in freshwater. Distinguishing characteristics were: 1) predominance of bicarbonate among the anions — accounting for > 90% of the negative equivalents in two-thirds of the waterbodies, 2) the near absence of sulfates — accounting for < 1 % of the anions in half the samples so that chloride exceeded sulfate (as meq/L) in three-fourths of the waters tested and 3) calcium was the dominant cation, although in certain waters the relative proportion of either magnesium or the monovalent cations was much higher than the world average. Regional patterns in water chemistry were apparent and are largely explained by differences in local geology, inputs from artesian wells or extensive use by humans. Most ionic salinity values were <400 mg/L. Using conventional criteria to assess trophic state, most water-bodies were eutrophic or hypereutrophic when judged by total phosphorus and chlorophyll content but as a whole the lakes sampled were low in nitrogen. Nitrogen: phosphorus ratios (generally < 10) and a significant empirical relation for chlorophyll-nitrogen provide evidence that nitrogen limited algal biomass. Secchi transparency values indicate light regimes were affected by nonalgal materials.

Uptake of lead from aquatic sediment by submersed macrophytes and crayfish

Uptake of lead (Pb) by submersed aquatic macrophytes and crayfish exposed to artificially contaminated pond sediment was measured under laboratory conditions. Macrophytes accumulated Pb in root tissue and foliage. Internal transport of Pb by plants was not detected. Senescent macrophytes accumulated more lead than live plants. Crayfish exposed to contaminated sediment accumulated Pb principally through adsorption to the exoskeleton and lost Pb through molting, although internal uptake and elimination without molting was measurable. Exposure to Pb leached from sediment, surface to weight ratios, and frequency of molting seem to influence Pb uptake by crayfish.

Role of land cover and hydrology in determining nutrients in mid-continent reservoirs: implications for nutrient criteria and management

Abstract Effects of nutrient input, hydraulic flushing rate and depth on reservoir nutrients were examined in the mid-continent landscape of the Ozark Highlands and Plains in Missouri and Plains of southern Iowa. Regionally the clear south-to-north increase in reservoir nutrients, amounting to a 4-fold increase in median total phosphorus (TP) and 3-fold increase in median total nitrogen (TN), showed a strong cross-system pattern with cropland cover (a surrogate for nonpoint-source nutrient loss from agricultural watersheds) but not with an index of hydraulic flushing rate. Cropland accounted for variation in TP in the Ozarks (51%) and TN in all 3 regions (Ozarks 58%, Plains 41%, Iowa 27%). Flushing accounted for variation in TP in the Missouri Plains (49%) and Iowa (29%). Our models suggest large-scale nutrient reduction will require massive changes in land cover to reduce nutrient input. In the Missouri Plains, for example, reducing cropland from 60% to 30% reduces TP and TN by only about 20% when other factors are held constant. Hydrology places added limits on reducing reservoir nutrients; consistent with theory, TP values in Missouri Plains reservoirs effectively double between flushing rates of 0.25 and 2 at any given cropland value. Dramatic nutrient reduction in these reservoirs is unlikely, and the influential role of hydraulic flushing adds additional management challenges for compliance with regional nutrient criteria. The analyses suggest hydrology must be considered when setting nutrient criteria, and it would be unreasonable to establish criteria based on water bodies with long retention time and apply them to rapidly flushed lakes.

Chlorophyll Response to Nutrients and Non-algal Seston in Missouri Reservoirs and Oxbow Lakes

Abstract When unaggregated summer chlorophyll data (Chl) from 184 Missouri reservoirs are plotted against total phosphorus (TP) a ‘bow’ in the distribution develops among a group of points with low Chl:TP ratios (averaging <0.05). Low Chl:TP is mostly associated with turbid, nutrient-rich inflows in reservoirs across the entire trophic range. Non-algal seston (NAS) is our best metric of these inflows and is a co-variable in Chl-TP regressions. This influence is most prominent in years of high runoff and is distinctly seasonal, being most prevalent in early summer prior to full stratification. In late summer, inflows typically enter as subsurface density currents, and nitrogen accounts for more variation in Chl-TP than NAS. Neither variable, however, greatly influences the long-term relation between Chl and TP, which is linear, relatively consistent, and matches the global pattern. In several oxbow lakes, high NAS caused by sediment resuspension is a chronic condition; it seems neither light nor flushing greatly influence Chl: TP in these shallow systems, and values approximate the statewide average. Temporal variation in Chl:TP is demonstrated by daily samples (n=1676) from a single reservoir, with average variability, that covers about 94% of the statewide Chl and about a third of the TP range. The Chl-TP pattern in over half of Missouri reservoirs deviates somewhat from predictions based on cross-system regression models. Nonetheless, for 97% of the study reservoirs, long-term Chl is within a factor of two above or below model predictions, and most are within ±25%. Such differences are modest when compared to the temporal variation measured in an intensively studied reservoir.

INITIAL PERFORMANCE OF A HIGH CAPACITY SURFACE-FLOW TREATMENT WETLAND

The Columbia Wastewater Treatment Wetland (“Columbia Wetland”) is a constructed cattail wetland in the Missouri River floodplain outside Columbia, Missouri, USA. the wetland receives mixed primary and secondary effluent (≈60,000 m3 d−1, BOD5≈30 mg L−1, TSS≈13 mg L−1, NH4−N≈8 mg L−1) from a conventional treatment plant. During its first 6 years of operation (October 1994 through November 2000), the wetland received loadings of BOD5, COD, and NH4−N averaging 50 83, and 12 kg ha−1 d−1, respectively, of which averages of 74%, 30%, and 17%, respectively, were removed from the effluent. TSS (mean loading =21 kg ha−1 d−1) frequently increased in the wetland due to erosion and disturbance by waterfowl, but TSS removal efficiency increased with time and the development of macrophyte biomass and averaged 30% by 1998. The wetland typically removed >97% of fecal coliforms and fecal streptococcus, 36% of TN and 4% of TP. In comparison to other large treatment wetlands, BOD removal by the Columbia Wetland has been exceptionally efficient.

Effects of Aggregation on Chlorophyll-Phosphorus Relations in Missouri Reservoirs

ABSTRACT Using chlorophyll and phosphorus data from 119 Missouri reservoirs we show how data aggregation-averaging data into seasonal means or long-term lake means – influences our ability to make inferences from large-scale statistical regression analyses. We demonstrate the most obvious phenomenon of data aggregation, that relations between variables estimated from aggregated data are generally stronger than the same relations estimated from unaggregated data. Averaging reduces the often large variation in the response of chlorophyll to phosphorus (Chl-TP) that characterizes measurements of these variables in lakes. We also demonstrate that inferences made from statistical regression analyses apply only to situations that match the level of aggregation used to produce the model. Using lake means we found a strong positive Chl-TP relation. This strong cross-sectional pattern among lakes in the study, however, did not always reflect the relation of these variables to one another in individual lakes. And t...