An Evaluation of a Point Source Brine Discharge into a Riverine System and Implications for TDS Limitations

The North Fork Holston River (NFHR) below Saltville, Virginia, has been the subject of many studies due to years of contamination from a closed chloroalkali plant. In addition, a point source brine discharge high in total dissolved solids (TDS) may also be adversely affecting aquatic biota. This study assessed the toxicity of the brine discharge to selected test organisms, including two freshwater mussel species and also discusses implications for development of a TDS limit based on brine toxicity. Ceriodaphnia dubia was the most sensitive organism in acute and chronic brine toxicity tests. Bivariate analysis of the brine conductivity and C. dubia LC₅₀ values showed no relationship (p = .1756); however, LC₅₀ values were strongly related (r² = 0.8818) to sodium concentrations in the brine discharge. A comparison of the results from acute tests with the brine effluent and the reference toxicant sodium chloride (NaCl) demonstrated that organisms were more sensitive to NaCl. Brine discharge toxicity to C. dubia was variable during the study duration with toxicity determined to be dependent on specific TDS constituents rather than conductivity or TDS. These results suggest the need for site-specific development of TDS criteria that are based on the specific constituents in a discharge.     

Influences of water chemistry on the acute toxicity of lead to Pimephales promelas and Ceriodaphnia dubia

The acute toxicity of lead (Pb) was examined for fathead minnows (Pimephales promelas; 96-h) and daphnids (Ceriodaphnia dubia; 48-h) in waters modified for hardness (as CaSO₄), dissolved organic carbon (DOC; as Aldrich humic acid) and alkalinity (as NaHCO₃) for parameterization of an acute freshwater biotic ligand model (BLM). Additionally, acute (96-h) and chronic (30-d) bioassays were performed for P. promelas to more clearly define the influence of pH (5.5–8.3) on Pb toxicity as modified by addition of HCl or NaOH using an automated titration system. Results indicate that Ca²⁺ is protective against acute Pb toxicity to P. promelas but not C. dubia. Strong protection was afforded by DOC and NaHCO₃ against acute Pb toxicity to P. promelas, whereas milder protection was observed for C. dubia with both parameters. Dissolved Pb LC50s from the P. promelas pH bioassays revealed a complex effect of pH on Pb toxicity, likely explained in part by Pb speciation and the competitive interaction of H⁺ with ionic Pb²⁺. Chronic pH bioassays also demonstrated that 30-d growth is not impaired in fathead minnows at relevant Pb concentrations. The findings reported herein suggest that development of separate BLMs for P. promelas and C. dubia should be considered.     

Identifying the Cause of Toxicity of a Saline Mine Water

Elevated major ions (or salinity) are recognised as being a key contributor to the toxicity of many mine waste waters but the complex interactions between the major ions and large inter-species variability in response to salinity, make it difficult to relate toxicity to causal factors. This study aimed to determine if the toxicity of a typical saline seepage water was solely due to its major ion constituents; and determine which major ions were the leading contributors to the toxicity. Standardised toxicity tests using two tropical freshwater species Chlorella sp. (alga) and Moinodaphnia macleayi (cladoceran) were used to compare the toxicity of 1) mine and synthetic seepage water; 2) key major ions (e.g. Na, Cl, SO₄ and HCO₃); 3) synthetic seepage water that were modified by excluding key major ions. For Chlorella sp., the toxicity of the seepage water was not solely due to its major ion concentrations because there were differences in effects caused by the mine seepage and synthetic seepage. However, for M. macleayi this hypothesis was supported because similar effects caused by mine seepage and synthetic seepage. Sulfate was identified as a major ion that could predict the toxicity of the synthetic waters, which might be expected as it was the dominant major ion in the seepage water. However, sulfate was not the primary cause of toxicity in the seepage water and electrical conductivity was a better predictor of effects. Ultimately, the results show that specific major ions do not clearly drive the toxicity of saline seepage waters and the effects are probably due to the electrical conductivity of the mine waste waters.     

Radionuclides in plants growing on sludge and water from uranium mine water treatment

Chemical treatment of uranium mine acid drainage generates sludge containing high radioactivity levels with, for example, ²³⁸U and ²²⁶Ra concentrations at about 18 and 9 kBq kg⁻¹ dry weight, respectively. Spontaneous vegetation, such as grass (Polygonum sp.), reeds (Phragmites australis), and bullrush (Typha latifolia) growing in sludge dewatering ponds concentrated uranium and uranium daughter radionuclides. However, bullrush growing in natural wetlands by the stream receiving treated mine water discharges contained even higher radionuclide concentrations, e.g., 21 Bq kg⁻¹ dry weight of ²³⁸U, about four times higher than bullrush growing on sludge, probably because the uranium in water is more bioavailable to Typha than uranium in the chemical sludge. It is suggested that wetlands with plant species could be used as a secondary treatment to further reduce radioactivity in chemically treated uranium mine water and to improve water quality in streams receiving treated water discharges. Furthermore, it is concluded that vegetation both from sludge drying ponds and from streams receiving treated water discharges, due to the high radionuclide concentrations in the vegetation, is not suitable as cattle feeding.     

Wastewater Treatment Effluent Reduces the Abundance and Diversity of Benthic Bacterial Communities in Urban and Suburban Rivers

In highly urbanized areas, wastewater treatment plant (WWTP) effluent can represent a significant component of freshwater ecosystems. As it is impossible for the composition of WWTP effluent to match the composition of the receiving system, the potential exists for effluent to significantly impact the chemical and biological characteristics of the receiving ecosystem. We assessed the impacts of WWTP effluent on the size, activity, and composition of benthic microbial communities by comparing two distinct field sites in the Chicago metropolitan region: a highly urbanized river receiving effluent from a large WWTP and a suburban river receiving effluent from a much smaller WWTP. At sites upstream of effluent input, the urban and suburban rivers differed significantly in chemical characteristics and in the composition of their sediment bacterial communities. Although effluent resulted in significant increases in inorganic nutrients in both rivers, surprisingly, it also resulted in significant decreases in the population size and diversity of sediment bacterial communities. Tag pyrosequencing of bacterial 16S rRNA genes revealed significant effects of effluent on sediment bacterial community composition in both rivers, including decreases in abundances of Deltaproteobacteria, Desulfococcus, Dechloromonas, and Chloroflexi sequences and increases in abundances of Nitrospirae and Sphingobacteriales sequences. The overall effect of the WWTP inputs was that the two rivers, which were distinct in chemical and biological properties upstream of the WWTPs, were almost indistinguishable downstream. These results suggest that WWTP effluent has the potential to reduce the natural variability that exists among river ecosystems and indicate that WWTP effluent may contribute to biotic homogenization.     

Effects of clay discharges on streams

The impact of clay discharges on benthic invertebrates was investigated by comparison of communities upstream and downstream of alluvial gold mining on 6 streams on the West Coast of the South Island, New Zealand. Mean turbidity was increased by 7–154 NTU above background (mean 1.3–8.2 NTU) by the mine discharges during the 2 months before sampling. Patterns of increase in suspended solids (strongly correlated with turbidity, r=0.95) were similar. Invertebrates densities were significantly lower at all downstream sites, ranging from 9 to 45% (median 26%) of densities at matched upstream sites. Downstream densities as a proportion of those upstream were negatively correlated with the logarithm of the turbidity loading (r=–0.82, P<0.05). The densities of the common taxa were also generally lower downstream of mining. Taxonomic richness was significantly lower at downstream sites in the four streams receiving higher turbidity loads (mean turbidity increase = 23–154 NTU). Lower epilithon biomass and productivity, and degraded food quality at the downstream sites probably explain the lowered invertebrate densities. At some sites, reduced bed permeability and interstitial dissolved oxygen, and avoidance reactions of invertebrates (i.e., increased drift), may have also contributed to lower invertebrate densities.Formerly DSIR Marine and Freshwater.     

How much do valley fills influence headwater streams?

Valley fill mining has the potential to alter headwater stream habitat in many areas in the eastern United States. In valley fill mining, overburden is removed to expose underlying coal seams. The overburden is then deposited in the adjacent valley. The deposited overburden from mining increases sedimentation, increases stream conductivity, and alters hydrologic regimes downstream of the fill. Changes in downstream communities are not well documented. However, it was suspected the increased sedimentation and conductivity would have deleterious effects upon the downstream macroinvertebrate communities. In southern West Virginia, four pairs of streams, each consisting of a fill and a reference stream, were selected as representative of watersheds experiencing valley fill mining. Stream pairs were selected for similar environmental conditions, with one stream having a valley fill in its headwaters. Each stream was sampled by replicate Surber samples (n=9 per stream). Water chemistry and sediment measurements also were taken at each location. Valley fill streams experienced significantly higher specific conductance (p < 0.01), but did not have elevated levels of fine sediment. Fills exhibited elevated levels of Na, K, Mn, Mg, Ca, Ni and Fe relative to reference streams. Additionally, valley fill streams demonstrated significantly lower densities of Ephemeroptera, Coleoptera, Odonata, Non-insects, Scrapers, and Shredders (p < 0.03) than reference streams. Further, Ephemeroptera richness was negatively related to specific conductivity and many of the richness metrics were negatively related to metals, both of which were generally elevated in fill streams. It appears that at the minimum, valley fills increase specific conductance and metals in streams and this or some other unqualified factors structure the macroinvertebrate community downstream of the valley fill. However, given the level of disturbance in valley fills, it is surprising how little differences existed between fills and reference stream biota.     

Exploring the legacy effects of surface coal mining on stream chemistry

Surface coal mining results in dramatic alterations of the landscape in central Appalachia, leading to a myriad of environmental problems. In this study, we explore the long-term effects of surface coal mining on stream chemistry and endeavor to gain a better understanding of the efficacy of reclamation. We examined 30 sites in the Raccoon Creek watershed in southeastern Ohio, where the majority of surface mine sites are in various stages of reclamation. Our results show that conductivity (r = 0.862; P = 0.000), sulfate (r = 0.619; P = 0.000), and aluminum (r = 0.469; P = 0.009) levels increase linearly as a function of the areal extent of reclaimed mines in each subwatershed, suggesting limited success of reclamation to restore natural stream chemistry. In contrast, pH was not significantly linearly correlated with the areal extent of surface mines. This suggests that local acid mine drainage remediation projects are able to regulate acidity levels in the watershed but not conductivity and certain heavy metal concentrations. Many sites had conductivity levels high enough to impair aquatic biota via ionic and osmoregulatory stress. In sum, surface coal mining appears to have a strong legacy effect on stream chemistry in the Raccoon Creek watershed.     

Structural and functional aspects of treated mine water and aquaculture effluent streams

Multiple effluent streams may flow into a single receiving stream making it difficult to understand the effects of a single effluent source or the interactions between effluents. In this study, we examined benthic community structure and function in an effluent stream formed by the release of treated mine water, in treated mine water that had been used as a water source for flow-through aquaculture and below the confluence of the two. This study demonstrated that macroinvertebrate communities, while taxonomically simple, developed in treated mine water. The addition of aquaculture effluent to the treated mine water allowed colonization by additional taxa, increased leaf decomposition rates and may have conferred resistance to a turbidity event. Ecosystem responses were mediated by the surrounding terrestrial environment. In shaded conditions macroinvertebrate densities could be as much as 10× higher and the taxa were dominated by simuliids and chironomids, while in open conditions filamentous algae flourished and the taxa were dominated by hydroptilids and chironomids. Consequently, consideration of stream processes that promote preferred ecological processes, such as macroinvertebrate production and organic matter processing, when siting effluent streams may reduce impacts on receiving streams.     

Effects of Salmon-Derived Nutrients and Habitat Characteristics on Population Densities of Stream-Resident Sculpins

Movement of nutrients across ecosystem boundaries can have important effects on food webs and population dynamics. An example from the North Pacific Rim is the connection between productive marine ecosystems and freshwaters driven by annual spawning migrations of Pacific salmon (Oncorhynchus spp). While a growing body of research has highlighted the importance of both pulsed nutrient subsidies and disturbance by spawning salmon, their effects on population densities of vertebrate consumers have rarely been tested, especially across streams spanning a wide range of natural variation in salmon densities and habitat characteristics. We studied resident freshwater prickly (Cottus asper), and coastrange sculpins (C. aleuticus) in coastal salmon spawning streams to test whether their population densities are affected by spawning densities of pink and chum salmon (O. gorbuscha and O. keta), as well as habitat characteristics. Coastrange sculpins occurred in the highest densities in streams with high densities of spawning pink and chum salmon. They also were more dense in streams with high pH, large watersheds, less area covered by pools, and lower gradients. In contrast, prickly sculpin densities were higher in streams with more large wood and pools, and less canopy cover, but their densities were not correlated with salmon. These results for coastrange sculpins provide evidence of a numerical population response by freshwater fish to increased availability of salmon subsidies in streams. These results demonstrate complex and context-dependent relationships between spawning Pacific salmon and coastal ecosystems and can inform an ecosystem-based approach to their management and conservation.     

Sublethal Toxicity Testing of Canadian Metal Mining Effluents: National Trends and Site-Specific Uses

As part of the Canadian Environmental Effects Monitoring program under the National Metal Mining Effluent Regulation, there is a requirement to conduct sublethal toxicity tests twice per year for the first three years. These first three years (2003 to 2005) were considered a period of initial monitoring and resulted in test endpoints for each of the required standardized methods on a fish, an aquatic plant, an invertebrate, and an algal species. On a national level (based on 1648 valid results), the test from most to least sensitive was: the inhibition of reproduction with Ceriodaphnia dubia, the growth inhibition (frond number) with Lemna minor, the inhibition of cell yield with Pseudokirchneriella subcapitata, the growth inhibition (dry weight) with Lemna minor, the growth inhibition of fathead minnows, and the effect on embryo viability with rainbow trout. This sensitivity ranking changed when tests were further evaluated on a geographical region and mine-type basis (e.g., base metal, precious metal, uranium, iron ore). Site-specific examples show how sublethal toxicity data are being used to track changes in effluent quality, choosing a final discharge point, monitoring multiple discharges to the same watercourse, and to identify study design weaknesses by comparing laboratory results to field survey conclusions.     

Metabolic regimes of three mid-order streams in southern Ontario,Canada exposed to contrasting sources of nutrients

Light, temperature, and discharge control stream metabolism, but the response of gross primary production (GPP) and ecosystem respiration (ER) to seasonal variation in these physical drivers may differ in accordance with the types of human activities present in the catchment. Our study examined three mid-order streams in southern Ontario, Canada that differed in anthropogenic nutrient sources (i.e., sewage treatment plant effluent, sewage lagoon effluent, and agriculture), but had comparable light, temperature, and discharge regimes. For each stream, GPP and ER were estimated daily from June through November. Comparisons of paired daily metabolic rates revealed pairwise differences among all streams, with streams receiving sewage effluent having greater rates and variability of GPP and ER than the stream draining agricultural land. The two sewage influenced streams differed only in ER. Temporal patterns of GPP and ER were correlated for all streams throughout the study period and were most affected by seasonal variation in temperature, whereby effluent receiving streams responded more rapidly to increases in temperature. Our findings suggest that managers may need to balance effects of human activities with regional environmental constraints on stream metabolism to maintain and enhance the ecological condition and services of stream ecosystems.

     

Water Quality of Effluent-dominated Ecosystems: Ecotoxicological, Hydrological, and Management Considerations

In arid and semi-arid regions of the southwestern United States and other parts of the world, flows of historically ephemeral streams are now perennially dominated by municipal and/or industrial effluent discharges, particularly in urbanized watersheds. Because effluent-dominated and dependent water bodies have previously received limited scientific study, we reviewed select contemporary topics associated with water quality of ephemeral streams receiving effluent flows. Our findings indicate that these ecosystems present numerous challenges to aquatic scientists and water resources managers, including: 1) appropriate ecosystems or upstream conditions used reference sites in biomonitoring are difficult to locate or do not exist; 2) water quality criteria, particularly for metals, are dramatically influenced by unique site-specific stream and land use conditions; 3) effluent-dominated streams represent worse-case scenarios for evaluating and predicting aquatic responses to emerging contaminants (e.g., pharmaceuticals and personal care products); 4) low-flow and drought conditions often preclude effective biomonitoring and water quality interpretation, or skew ambient assessment results; 5) chemical-physical water quality parameters (e.g., dissolved oxygen, conductivity, temperature) are dramatically altered by effluent and stormwater characteristics; and 6) beneficial reuse of reclaimed effluent waters potentially conflict with sustainability of ecological integrity. Subsequently, we recommend several water quality research priorities for effluentdominated water bodies.     

Acute Toxicity of TiO2 Nanoparticles to Ceriodaphnia dubia under Visible Light and Dark Conditions in a Freshwater System

The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO₂ NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO₂ NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO₂ NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining.     

Dissolved phosphorus concentrations and sediment interactions in effluent–dominated Ozark streams

Phosphorus (P) loads from point sources have a significant influence on dissolved P concentrations in streams and sediment-water column dynamics. The goal of this study was to quantify dissolved P concentrations and sediment-P interactions in Ozark (USA) headwater streams with high point source P loads. Specifically, the objectives were to: (1) compare soluble reactive P (SRP) upstream and downstream from wastewater treatment plant (WWTP) effluent discharges; (2) examine longitudinal gradients in SRP downstream from WWTPs; (3) evaluate the effect of WTTP P inputs on sediment-water column P equilibrium and sediment exchangeable P. Water and sediment samples were collected, extracted and analyzed from July 2002 through June 2003 at these Ozark streams. Mean SRP concentrations in the select Ozark streams were significantly greater downstream from effluent discharges (0.08–2.10 mg L⁻¹) compared to upstream (0.02–0.12 mg L⁻¹). Effluent discharge from the WWTPs increased equilibrium concentrations between stream sediments and the water column; mean sediment equilibrium P concentration (EPC₀) was between 0.01–0.07 mg L⁻¹ upstream from WWTP and the increase downstream was proportional to that observed in water column SRP. Sediment exchangeable P (EXP) was greater downstream from the effluent discharges (0.3–6.8 mg kg⁻¹) compared to upstream (0.03–1.4 mg kg⁻¹), representing a substantial transient storage of P inputs from WWTPs. Furthermore, P was generally not retained in these stream reaches when dilution was considered using a hydrologic tracer and was released in one stream reach where effluent P concentrations decreased over the study period. Thus, the effect of the WWTPs was profound in these streams increasing water column and sediment-bound P, and also reducing the ability of these stream reaches to retain P. In P-enriched streams, effluent P discharges likely regulate sediment and aqueous phase P equilibrium and sediment bioavailable P, not the sediments.     

Nutrients related to the hydrologic regime in the coastal lagoons of Viladecans (NE Spain)

This study presents the major water characteristics of the Viladecans coastal lagoons in the Llobregat Delta (NE Spain), and the interpretation of their functional relationships with freshwater discharges. Ranges of conductivity show that Murtra, Remolar and Vidala are strongly influenced by freshwater. A second group (Reguerons, Braç Vidala) is characterised by brackish water with intermediate values of conductivity. In contrast, the lower part of the water column of Remolar and Vidala is quite salty water. A permanent pycnocline is established causing meromixis. Finally in Sant Climent a great variation is observed from fresh to seawater. Nutrient inputs are related to freshwater discharges. The range of DIN/SRP ratios observed (0.1–71) shows that a great variety of biogeochemical processes take place in these lagoons. High DIN/SRP ratios occur in water masses receiving high freshwater discharges (Murtra, Remolar and Vidala surface). In contrast, low DIN/SRP ratios correspond to water masses (Reguerons, Braç Vidala, Sant Climent) receiving water discharges from the groundwater and to those in the lower part of the water column of Remolar and Vidala. The SRP and DIN concentrations of the water in Remolar, Vidala and Murtra are very high (higher than any other with similar morphological characteristics in Spain). However, the trophic state of Reguerons, Sant Climent and Braç Vidala is lower. The data presented indicate that the Viladecans coastal lagoons are in a hypereutrophic state, as the result of receiving over a long period of time nutrient discharges associated to man-made freshwater inputs higher than their carrying capacity or capacity to metabolise the nitrogen and phosphorus discharges. Remedial measures should include reducing nutrient discharges into the lagoons and favouring water turnover in the lagoons.     

The effect of dissolved oxygen,sediment, and sewage treatment plant discharges upon growth,survival and density of Asiatic clams

The biology of Corbicula fluminea, the Asiatic clam, in the Vermilion River, Louisiana, as affected by sediment, dissolved oxygen (DO) levels, and sewage treatment plant (STP) effluents was investigated. A point source of high DO water to the Vermilion River established a gradient of DO that decreased as the river moved towards the Gulf of Mexico. Lowering DO levels were exacerbated by municipal sewage treatment plant discharges in the 20 km reach studied. Low dissolved oxygen was associated with reduced Corbicula density in the river and 30-day in-stream growth studies (weight and length) demonstrated that low DO inhibited growth. Generally, if DO was < 1.0 mg l^–1 in sediment pore water and/or < 3.0 mg l^–1 at the sediment-water interface, growth was significantly impaired (p < 0.05). Corbicula experienced substantial mortality near the STP discharges (up to 70% in 30 days) and laboratory toxicity tests with Ceriodaphnia dubia, a sensitive cladoceran, also strongly suggested discharges were chronically toxic at 6.25–25.0% effluent. Respiration experiments along with environmental measurements of DO, temperature, and STP discharge chemistry support a hypothesis that clam populations are adversely affected by the suite of environmental conditions present in the Vermilion River. Further, growth studies were consistent with observed population densities in situ.     

Diatom community response to an acid mine drainage gradient

Acid mine drainage (AMD) is a significant environmental issue worldwide. On the West Coast of the South Island, New Zealand, many AMD-affected streams occur within close proximity to naturally acidic streams, enabling us to compare the response of communities in naturally and anthropogenic acidified systems. We investigated epiphytic diatom communities in 39 streams along an AMD gradient that included naturally acidic and circum-neutral reference streams. There was a wide range in taxonomic richness in reference streams and those moderately impacted by AMD (8–33 taxa). Taxonomic richness was greatly reduced in severely impacted streams (1–5 taxa) at a threshold of pH 3.4 and was dominated by Pinnularia cf. acidophila (69–100% relative abundance). Community composition differed between circum-neutral reference streams and moderately and severely impacted streams. However, naturally acidic and moderately impacted streams had similar diatom communities primarily composed of Eunotia and Frustulia species. Our results indicate that diatom communities are strongly structured by pH and able to tolerate moderate conductivity and metal concentrations. This is a challenge for researchers and water managers attempting to incorporate diatoms into AMD monitoring in regions with naturally acidic streams.     

Temporal dynamics of benthic macroinvertebrate communities and their response to elevated specific conductance in Appalachian coalfield headwater streams

Coal mining in central Appalachia USA causes increased specific conductance in receiving streams. Researchers have examined benthic macroinvertebrate community structure in such streams using temporally discrete measurements of SC and benthic macroinvertebrates; however, both SC and benthic macroinvertebrate communities exhibit intra-annual variation. Twelve central Appalachian headwater streams with reference quality physical habitat and physicochemical conditions (except for elevated SC in eight streams) were sampled ≤fourteen times each between June 2011 and November 2012 to evaluate benthic macroinvertebrate community structure. Specific conductance was recorded at each sampling event and by in situ data loggers. Streams were classified by mean SC Level (Reference, 17–142 μS/cm; Medium, 262–648 μS/cm; and High, 756–1535 μS/cm). Benthic macroinvertebrate community structure was quantified using fifteen metrics selected to characterize community composition and presence of taxa from orders Ephemeroptera, Plecoptera, and Trichoptera. Metrics were analyzed for differences among SC Levels and months of sampling. Reference streams differed significantly from Medium-SC and High-SC streams for 11 metrics. Medium-SC streams had the most metrics exhibiting significant differences among months. Relative abundances of Plecoptera and Trichoptera were not sensitive to SC, as the families Leuctridae and Hydropsychidae exhibited increased relative abundance (vs. reference) in streams with elevated SC. In contrast, Ephemeroptera richness and relative abundance were lower, relative to reference, in elevated-SC streams despite increased relative abundance of Baetidae. Temporal variability was evident in several metrics due to influence by taxa with seasonal life cycles. These results demonstrate that benthic macroinvertebrate communities in elevated-SC streams are altered from reference condition, and that metrics differ in SC sensitivity. The time of year when samples are taken influenced measured levels and differences from reference condition for most metrics.     

Growth and physiological responses of Kandelia candel and Bruguiera gymnorrhiza to livestock wastewater

Growth and physiological responses of two mangrove species (Kandelia candel and Bruguiera gymnorrhiza) to livestock wastewater under two salinity conditions (seawater with salinity of 30þ and freshwater) were examined in greenhouse pot-cultivation systems for 144 days. Wastewater treatment significantly enhanced growth of Kandelia candel and Bruguiera gymnorrhiza in terms of stem height, stem basal diameter, leaf production, maximum unit leaf area and relative growth rate. Wastewater discharges and salinity levels did not significantly change biomass partitioning of Kandelia candel, however, more biomass of Bruguiera gymnorrhiza was allocated to leaf due to wastewater discharges. In Bruguiera gymnorrhiza, contents of chlorophyll a and chlorophyll b increased with wastewater discharges but such increase was not observed in Kandelia candel. On the other hand, livestock wastewater increased leaf electric conductance in Kandelia candel but not in Bruguiera gymnorrhiza. The peroxidase activity in stem and root of Kandelia candel under both salinity conditions increased due to wastewater discharges, while the activity in root of the treated Bruguiera gymnorrhiza seedlings decreased under freshwater condition but increased at seawater salinity. The superoxide dismutase activity in treated Bruguiera gymnorrhiza decreased but did not show any significant change in Kandelia candel receiving livestock wastewater.