Non-volatile Suspended Solids Research Articles

Trophic state and limiting nutrient evaluations using trophic state/level index methods: a case study of Borçka Dam Lake.

The relationships between nutrients and the trophic state of Borçka dam reservoir in the Çoruh River Basin, which is located in the Eastern Black Sea region of Turkey, were evaluated using the trophic state index (TSI), trophic level index (TLI), and statistical analysis. The samples data were analyzed for chlorophyll-a (Chl-a), total phosphorus (TP), total nitrogen (TN), and secchi disk (SD). In the evaluation, according to the TSI' TLI and Turkish legislation, the reservoir is assessed as mesotrophic in terms of TP, TN data of the water quality. The measurement results of these parameters are higher at the depth points and lower on the surface. The Chl-a parameter is evaluated mesotrophic with 2013 data at the depth, and oligotrophic with 2016 data. The result of TSI (Chl-a) < TSI (SD), TSI (Chl-a) < TSI (TP), and TSI (TN) indicate non-algal turbidity. At the same time, this was verified by calculating the non-algal turbidity coefficient (Kna). It is observed that there is a low correlation between Chl-a and Kna, however a low correlation with TN, and a high correlation with TP. Non-algal particles in the dam lake may occur due to surface runoff and soil erosion from the agricultural area and human settlements. Regression analysis was conducted to determine the relationship between nutrients and Chl-a. The relationship of Chl-a concentration with TN, TP, and TN/TP concentrations is weak. This supports that there are inorganic suspended solids (non-volatile suspended solids) with high underwater light availability.Graphical abstract.

Bison and Cattle Grazing Impacts on Baseflow Suspended Sediment Concentrations within Grassland Streams

Prior to European colonization and the introduction of cattle, bison were the prominent grazing ungulates throughout North American grasslands. Yet, relative zoogeomorphic impacts between bison and cattle on grassland streams remain largely unknown. Utilizing a paired watershed study design, we compared baseflow suspended sediment concentrations across ten watersheds and four grazing treatments (ungrazed, bison-grazed, moderately stocked cattle-grazed, and intensively stocked cattle-grazed) in the Flint Hills subregion of the Great Plains. Additionally, we determined whether periods of increased thermal stress led to higher sediment concentrations within each treatment. Water samples were analyzed for total suspended solids (TSS, mg/L), nonvolatile suspended solids (NVSS, mg/L), and percentage organic matter (POM, percent). Intensively stocked cattle-grazed treatments produced significantly higher TSS and NVSS concentrations relative to ungrazed (TSS p = 0.012, NVSS p < 0.01) and bison-grazed treatments (TSS p = 0.082, NVSS p < 0.01). Moderately stocked cattle-grazed treatments contained significantly higher NVSS concentrations relative to bison-grazed treatments (p = 0.057). Bison-grazed and ungrazed treatments contained similar sediment concentrations (TSS and NVSS p > 0.10). Additionally, intensively and moderately stocked cattle-grazed treatments showed a significant increase in sediment concentrations with increasing temperature (p = 0.024 and p = 0.08, respectively), whereas bison-grazed and ungrazed treatments did not (p > 0.10). At the subdaily timescale, the highest sediment concentrations within cattle-grazed treatments and the greatest difference in sediment concentrations between cattle-grazed and ungrazed treatments coincided with the hottest daily temperatures, further highlighting that cattle-grazing impacts are influenced by thermal conditions.

Effects of sediments and coloured dissolved organic matter on remote sensing of chlorophyll-a using Landsat TM/ETM+ over turbid waters

ABSTRACTRemote sensing of chlorophyll-a is challenging in water containing inorganic suspended sediments (i.e. non-volatile suspended solids, NVSS) and coloured dissolved organic matter (CDOM). The effects of NVSS and CDOM on empirical remote-sensing estimates of chlorophyll-a in inland waters have not been determined on a broad spatial and temporal scale. This study evaluated these effects using a long-term (1989–2012) data set that included chlorophyll-a, NVSS, and CDOM from 39 reservoirs across Missouri (USA). Model comparisons indicated that the machine-learning algorithm BRT (boosted regression trees, validation Nash–Sutcliffe coefficient = 0.350) was better than linear regression (validation Nash–Sutcliffe coefficient = 0.214) for chlorophyll-a estimate using Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) imagery. Only a small proportion of BRT model residuals could be explained by sediments or CDOM, and the observed trends in BRT residuals were different from the theoretical effects expected from NVSS and CDOM. Our results also indicated a small systematic bias by the BRT model, but it was not likely caused by NVSS or CDOM.

Influence of temperature on sludge settleability and bacterial community structure in enhanced biological phosphorus removal systems

In this study, the influence of temperature on sludge settleability and bacterial community structure was investigated in two EBPR systems for a better understanding of the seasonally variable settleability. The results indicated that settleability depended both on the filament content and on the non-soluble phosphorus (Pns) and non-volatile suspended solids (NVSS) contents at varying temperatures. When the temperature was increased, settleability was significantly improved because of the substantial reduction in the filaments. When the temperature was decreased, settleability changed slightly in the long run and was mainly determined by Pns/VSS and NVSS/VSS (p < 0.05). Canonical correspondence analysis results indicated that bacterial community structure was significantly correlated with temperature and settleability (p < 0.01). At a high temperature (25°C), 21 species mostly affiliated with Proteobacteria, followed by Bacteroidetes, were stimulated greatly. The proliferation of Bacteroidetes might have a close relation with the improvement of settleability. At a low temperature (15°C), 25 species which were different from that at a high temperature proliferated in the system. These species mostly affiliated with Proteobacteria, followed by Actinobacteria. The large population of Actinobacteria was closely correlated with poor settleability. This work provides a valuable basis for the control of seasonal sludge bulking in EBPR systems.

Airborne hyperspectral remote sensing to assess spatial distribution of water quality characteristics in large rivers: The Mississippi River and its tributaries in Minnesota

Aircraft-mounted hyperspectral spectrometers were used to collect imagery with high spatial and spectral resolution for use in measuring optically active water quality characteristics of major rivers of Minnesota. Ground-based sampling undertaken concurrent with image acquisition provided calibration data for chlorophyll, suspended solids, turbidity and other measures of water clarity. Our approach identified the spectral characteristics that distinguish waters dominated by several inherent optical properties (IOPs), and we used those characteristics to develop models to map water quality characteristics in optically complex waters. For phytoplankton related variables (volatile suspended solids (VSS) and chlorophyll a (chl a)), the ratios of the scattering peak at the red edge (~700nm) with the reflectance troughs caused by chlorophyll absorption at ~670nm and other plant pigment absorption peaks at 592 and 620nm all were strong predictors of chl a and VSS (r2 values of 0.73–0.94). The scattering peak at ~700nm was a strong predictor of variables related to water clarity (total suspended solids (TSS), turbidity and turbidity tube (T-tube)) (r2 values of 0.77–0.93). For mineral-based variables (nonvolatile suspended solids (NVSS) and the ratio NVSS:TSS), combinations of the TSS and chl a relationships described above were strong predictors (r2 values of 0.73–0.97) and the most robust because this model corrects for the scattering of phytoplankton at ~700nm. Application of the methods to quantify spatial variations in water quality for stretches of the Mississippi River and its tributaries indicate that hyperspectral imagery can be used to distinguish and map key variables under complex IOP conditions, particularly to separate and map inorganic suspended sediments independently of chlorophyll levels.

Comparative Study of Hops-Containing Products on Human Cytochrome P450-Mediated Metabolism

The potential for 15 different ales (6), ciders (2 apple and 1 pear), and porters (6) and 2 non-alcoholic products to affect cytochrome P450 (CYP)-mediated biotransformation and P-glycoprotein-mediated efflux of rhodamine was examined. As in our previous study, a wide range of recovered nonvolatile suspended solids dry weights were noted. Aliquots were also found to have varying effects on biotransformation and efflux. Distinct differences in product ability to affect the safety and efficacy of therapeutic products confirmed our initial findings that some porters (stouts) have a potential to affect the safety and efficacy of health products metabolized by CYP2D6 and CYP3A4 isozymes. Most products, except 2 of the ciders and the 2 non-alcoholic products, also have the potential to affect the safety of CYP2C9 metabolized medications and supplements. Further studies are required to determine the clinical significance of these findings.

Temporal Asynchrony of Trophic Status Between Mainstream and Tributary Bay Within a Giant Dendritic Reservoir: The Role of Local-Scale Regulators

Limnologists have regarded temporal coherence (synchrony) as a powerful tool for identifying the relative importance of local-scale regulators and regional climatic drivers on lake ecosystems. Limnological studies on Asian reservoirs have emphasized that climate and hydrology under the influences of monsoon are dominant factors regulating seasonal patterns of lake trophic status; yet, little is known of synchrony or asynchrony of trophic status in the single reservoir ecosystem. Based on monthly monitoring data of chlorophyll a, transparency, nutrients, and nonvolatile suspended solids (NVSS) during 1-year period, the present study evaluated temporal coherence to test whether local-scale regulators disturb the seasonal dynamics of trophic state indices (TSI) in a giant dendritic reservoir, China (Three Gorges Reservoir, TGR). Reservoir-wide coherences for TSICHL, TSISD, and TSITP showed dramatic variations over spatial scale, indicating temporal asynchrony of trophic status. Following the concept of TSI differences, algal productivity in the mainstream of TGR and Xiangxi Bay except the upstream of the bay were always limited by nonalgal turbidity (TSICHL−TSISD <0) rather than nitrogen and phosphorus (TSICHL−TSITN <0 and TSICHL−TSITP <0). The coherence analysis for TSI differences showed that local processes of Xiangxi Bay were the main responsible for local asynchrony of nonalgal turbidity limitation levels. Regression analysis further proved that local temporal asynchrony for TSISD and nonalgal turbidity limitation levels were regulated by local dynamics of NVSS, rather than geographical distance. The implications of the present study are to emphasize that the results of trophic status obtained from a single environment (reservoir mainstream) cannot be extrapolated to other environments (tributary bay) in a way that would allow its use as a sentinel site.

Seasonal variability of biomass density and activated sludge settleability in full-scale wastewater treatment systems

Biosolids sedimentation is a critical component of the activated sludge wastewater treatment process. Seasonal variability of biomass settleability has been previously reported and linked to variable filament content in some studies, but others have reported seasonal variations without changes in filament content. Biomass density (mass per microbial floc volume, not including pore spaces) has recently been shown to vary substantially and to affect settleability in full-scale systems, but its potential role in seasonal variations has not been previously evaluated. Four full-scale activated sludge systems were monitored for density, filament content, and settleability for a year. Biomass density values were significantly higher in warm weather than in cold weather in all plants. Settleability was significantly worse in cold weather in three of the four systems, and the inverse of the buoyant density was correlated with settleability in these three systems. Filament content, on the other hand, exhibited seasonal variability and was correlated with settleability in only one of the four plants. Non-volatile suspended solids content was correlated with buoyant density and exhibited seasonal variability in all four systems. Biomass phosphorus content measurements suggested that seasonally variable enhanced biological phosphorus removal activity affected density in one of the systems. These results suggest that variable density plays a role in seasonally variable settleability in some full-scale wastewater treatment systems, they help to clarify previously unexplained reports of seasonally variable settleability that were independent of changes in filament content, and they provide the basis for development of strategies for improved performance.

Factors regulating trophic status in a large subtropical reservoir, China

We evaluated a 4-year data set (July 2003 to June 2007) to assess the trophic state and its limiting factors of Three-Gorges Reservoir (TGR), China, a large subtropical reservoir. Based on Carlson-type trophic state index (TSI)(CHL), the trophic state of the system was oligotrophic (TSI(S) < 40) in most months after the reservoir became operational, although both TSI(TP) and TSI(TN) were higher than the critical value of eutrophic state (TSI(S) > 50). Using Carlson's (1991) two-dimensional approach, deviations of the TSI(S) indicated that factors other than phosphorus and nitrogen limited algal growth and that nonalgal particles affected light attenuation. These findings were further supported by the significant correlation among the values of TSI(CHL) - TSI(SD) and nonvolatile suspended solids and water residence time. The logarithmic model showed that an equivalent TSI(CHL) and TSI(SD) could be found at tau = 54 days in the TGR (Fig. 7). Accordingly, nonalgal particulates dominated light attenuation and limited algal biomass of the reservoir when tau < 54 days.

Comparative Study of Hop-Containing Products on Human Cytochrome P450-Mediated Metabolism

Thirty-five national and international brands of beer were examined for their potential to affect human cytochrome P450 (CYP)-mediated metabolism. They represented the two main categories of beer, ales and lagers, and included a number of specialty products including bitter (porter, stout), coffee, ice, wheat, Pilsner, and hemp seed. Aliquots were examined for nonvolatile soluble solids, effect on CYP metabolism and P-glycoprotein (Pgp) transport, and major alpha- and beta-hop acids. Wide variance was detected in contents of alcohol, nonvolatile suspended solids, and hop acids and in the potential to affect CYP-mediated metabolism and Pgp-mediated efflux transport. Many of the products affected CYP2C9-mediated metabolism, and only two (NRP 306 and 307) markedly affected CYP3A4; hence, some products have the capacity to affect drug safety. CYP3A4, CYP3A5, CYP3A7, and CYP19 (aromatase) inhibition to the log concentration of beta-acid content was significant with r(2) > 0.37, suggesting that these components can account for some of the variation in inhibition of CYP metabolism.

Seasonal dynamics of suspended solids in a giant subtropical reservoir (China) in relation to internal processes and hydrological features

To explore the factors regulating seasonal variation of total suspended solids (TSS) and its two fractions in a giant dendritic reservoir (the Three-Gorges Reservoir of China, TGR) in the subtropical monsoon region, suspended solids, chlorophyll a (a surrogate for lake internal processes) and water residence time (an index of hydrologic flushing) were examined monthly from August 2005 to July 2006. TSS ranged from 0.6 to 200.3 mg/L and from 0.6 to 78 mg/L respectively in the mainstream and in a typical reservoir-bay (the Xiangxi Bay) of the TGR,. TSS exhibited a typical seasonal pattern in the mainstream rather than in the Xiangxi Bay of the TGR. The fraction of non-volatile suspended solids (NVSS) was often more dominant in the mainstream than in the Xiangxi Bay, especially during the flood season. Regressions analysis showed that 87.6% and 89.8 % of seasonal variation in TSS and NVSS of the mainstream, respectively, are explained by water residence time . In contrast, suspended solids (particularly volatile suspended solids, VSS) of the Xiangxi Bay displayed significant correlation with algal biomass, and no correlation with hydrological parameters. It implies that the Xiangxi Bay was a more autochthonous system than the mainstream of the TGR where exogenous influences were the more determinant factors.

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

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.

Microsphere addition for the study of biomass properties and density effects on settleability in biological wastewater treatment systems

Recent research has demonstrated that biomass density can vary in activated sludge systems, and that this can affect biomass settleability. Other factors related to floc structure are well known to affect settleability, and these can also vary considerably across samples. A new method to isolate density effects on sedimentation was developed and applied based on the addition of commercially available, high and low density microspheres. Density was a linear function of microsphere dose in five full-scale samples, and it was negatively correlated with sludge volume index (SVI) values. Density effects on SVI were similar to previous reports where density varied with biomass polyphosphate content. A new method to calculate water content and floc volume was developed and applied, and water content was inversely correlated with density, polyphosphate, and non-volatile suspended solids. These results suggest microsphere addition may be useful in future studies of biomass sedimentation and other properties.

Density effects on activated sludge zone settling velocities

A recently developed method to manipulate biomass density based on the addition of synthetic microspheres was used to isolate density effects on zone (hindered) settling velocities in samples from full-scale activated sludge plants over a range biomass densities and concentrations. Settling velocities increased by as much as a factor of five as density was increased by microsphere addition. The effects of density on the Vesilind sedimentation model parameters ( V= V oe − kX , where V is the settling velocity, X is the biomass concentration, and V o and k are constants) were evaluated. The parameter V o was positively correlated with density for values greater than approximately 1.02 g/mL, while k values were approximately constant in this range. New models were developed for settling velocity as a function of both density and biomass concentration, and these may be useful for future incorporation with clarifier models to improve predictions of system performance, particularly when biomass characteristics known to affect density are variable, such as polyphosphate and nonvolatile suspended solids content.

Causes of Variable Biomass Density and Its Effects on Settleability in Full-Scale Biological Wastewater Treatment Systems

Both variable biomass density and floc structure were determined to affect the settleability of microbial biomass produced during biological wastewater treatment (activated sludge). Average biomass density varied from 1.022 to 1.056 g/mL in a survey of 17 full-scale biological wastewater treatment systems with a variety of configurations. Biomass settleability was correlated with density in samples with higher filament contents and/or more open floc structures, but settleability was independent of density in biomass with lower filament contents and more rounded floc structures. Biomass density increased with polyphosphate content, and enhanced biological phosphorus removal (EBPR) plants had higher density and better settleability than non-EBPR plants, including two systems that converted to EBPR during the course of this study. Density also increased with increasing nonvolatile suspended solids content, which was linked both to polyphosphate and to increasing solids residence times. Both density and floc structure should be considered in future analyses of activated sludge settleability, and it may be possible to improve system performance by adopting a new set of operational and design strategies to increase density.

Recent Observation of a Proliferation of Ranunculus trichophyllus Chaix. in High-altitude Lakes of the Mount Everest Region

Large populations of the threadleaf water-crowfoot, Ranunculus trichophyllus, were discovered in several high-altitude lakes in the Himalayas of Nepal in which the species did not occur as recently as 1987. One of the study lakes, at 4760 m, is the highest altitude from which an aquatic angiosperm has been reported. A canonical discriminant analysis suggests that the key environmental factors differing between vegetated and non-vegetated lakes among a chain of five interconnected water bodies are length of the ice-free season, conductivity, non-volatile suspended solids, and bicarbonate. We believe, however, that an increased length of the ice-free season is likely the controlling factor in the recent invasion by Ranunculus trichophyllus. Its range expansion is likely a signal of a warming alpine climate in our study area.

Factors Affecting Iowa Lake and Reservoir Water Quality

ABSTRACT Iowa lake and reservoir water quality data collected during the summers of 1990 and 1992 were analyzed according to origin (lake vs. reservoir) and location, updating previous synoptic surveys. Morphometric comparisons between Iowa regions indicate unique characteristics for reservoirs, glacial lakes, oxbow lakes, and waterbodies on the Des Moines glacial lobe. All Iowa lakes and reservoirs are eutrophic although there is a significant range of water quality and within-region variability. Parameters such as chlorophyll a, total phosphorus (TP), and total nitrogen (TN) summer mean concentrations were highest on the Des Moines glacial lobe (means of 64 μg L−1, 164 μg L−1, and 4.4 mg L−1, respectively). A comparison of northern Iowa versus southern Minnesota lakes and southern Iowa versus northern Missouri reservoirs indicated that Iowa water quality is more eutrophic in both instances. Northern Iowa lakes had higher TN (3.0 mg L−1), total suspended solids (TSS, 39 mg L−1), and non-volatile suspended solids (NVSS, 18 mg L−1) summer mean concentrations than southern Minnesota lakes (2.1 mg L−1, 14 mg L−1, and 3 mg L−1, respectively). Southern Iowa reservoirs had higher TP (149 μg L−1), TN (1.8 mg L−1), TSS (34 mg L−1), and NVSS (25 mg L−1) summer mean concentrations than northern Missouri reservoirs (47 μg L−1, 0.7 mg L−1, 10 mg L−1, and 7 mg L−1, respectively).

Phytoplankton primary production and photosynthetic parameters in reservoirs along a gradient of watershed land use

We investigated how watershed land use (a gradient of agricultural vs. forested land) relates to phytoplankton primary production (PPr) and photosynthetic parameters in 12 reservoirs in Ohio and examined spatial variation in these parameters. Shallow sites near stream inflows had higher light attenuation, total phosphorus (TP), chlorophyll, nonvolatile suspended solids (NVSS), light‐saturated photosynthesis (PBm), and volumetric PPr than deeper sites near dam outflows, but areal PPr and the initial slope of the photosynthesis‐irradiance curve (αB) were not significantly different between sites. Mean mixed layer irradiance and the severity of light limitation did not differ between sites because shallower depths compensated for higher light attenuation at inflow sites. Watershed land use (percent agriculture) was only weakly (but significantly) related to mean annual PPr, TP, and chlorophyll, but there was a well‐defined upper limit to the effect of land use on all three of these parameters. Multiple regression showed that inclusion of additional watershed factors (the ratio of watershed land area to reservoir volume and the ratio of cropland area to number of livestock) greatly increased the variance explained compared to land use alone. TP and chlorophyll were highly correlated with each other and with PPr. Comparison of our TP‐chlorophyll, TP‐PPr, and chlorophyll‐PPr regressions with those of other studies suggests that reservoirs have lower PPr per unit TP than natural lakes, probably because of lower light intensity and higher concentrations of nonalgal P in reservoirs.

Submerged aquatic vegetation correlations with depth and light attenuating materials in a shallow subtropical lake

A 3-year study was done to quantify the biomass of submerged aquatic vegetation (SAV) and its relationship with environmental attributes in Lake Okeechobee, the largest lake in the southeastern United States. Plants were sampled on 21 occasions at sites located along 15 fixed transects around the shoreline, giving rise to 721 observations of SAV species (Chara spp., Vallisneria americana, Hydrilla verticillata, Potamogeton illinoinensis) dry weight biomass. Environmental sampling focused on factors that attenuate light, including phytoplankton chlorophyll a (chl a), total suspended solids (TSS), non-volatile suspended solids (NVSS) and color. Depth and Secchi transparency also were measured. Based on regression analysis, NVSS was considerably more important in attenuating light than chl a or color. Total biomass of SAV varied from 0 to 271 g dw m−2, with a mean of 4.7 g dw m−2, and strong dominance by Chara. The SAV biomass was lower than average for Florida lakes, and may reflect the influence of suspended solids on underwater irradiance, as well as high water level in the late 1990s. Dense SAV was found only where depth was < 2 m and TSS < 20–30 mg l−1. At locations where high biomass of SAV occurred, the plants may have influenced water quality, because concentrations of TSS, NVSS, and chl a were 2–3 fold lower than at sites with no plants. The potential effects of SAV also were apparent at a regional scale. The shoreline region of the lake displayed a pattern of rising and falling chl a and NVSS with water depth. This occurred both at sites with and without plants, suggesting that it may be driven by physical processes, such as water circulation patterns, which are influenced by depth. However, the pattern was dampened at sites with SAV, indicating a potential to influence these attributes of water quality.

INFLUENCE OF SEASONAL MONSOON ON THE TROPHIC STATE DEVIATION IN AN ASIAN RESERVOIR

Trophic parameters including total nitrogen (TN), total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) were analyzed to evaluate how the Asian monsoon influences the trophicstate of the Taechung Reservoir, Korea. By using conventional criteria, the trophic state of this system ranged from mesotrophic to hypertrophic with spatial and seasonal variationsdepending on landuse pattern and flow regime. Based on TP, CHL, and transparency, the overall trophic state declined from the headwaters to the dam. However, based on TN, the entire reservoir was hypereutrophic thoughout the year. Comparing nutrients and CHL as trophic parameters, large disparities of the trophic state have been observed in the headwaters during intensive monsoon. The trophic state was much greater when assessments were based on nutrients instead of CHL, indicating apotential trophic deviation. Using Carlson's (1990) twodimensional approach, deviations of the Trophic State Index(TSI), based on the relation between TSI (CHL) minus TSI(TP), and TSI (CHL) minus TSI (SD) during the intensivemonsoon indicated that factors other than phosphorus limitedalgal growth, and that non-algal particles affect lightattenuation. These findings were supported by high non-volatilesuspended solids (NVSS), short water residence time, and low CHL:TP ratios during monsoon. Such deviations, however, did not occur during weak monsoon. The trophic disparity during theintensive monsoon was considered to be a result of the shortwater retention time and reduced light availability throughdominance of inorganic suspended solids. Under these circumstances, trophic state assessments based only on nutrientloading may not be a useful indicator for water management.