Wastewater treatment at the Houghton Lake wetland: Temperatures and the energy balance

This paper describes the temperatures in surface water and soils in a very long-running study of the capacity of a natural peatland to remove nutrients from treated wastewater. Two zones were found, an adaptation zone near the discharge to the wetland, and a background zone comprised of areas more than about 100 m from the discharge. The discharge zone was transformed to a floating mat during the 30-year course of the project. Strong diurnal cycles in surface water temperatures were measured, with a median daily swing of about 6–10 °C. Pumped water was a few degrees warmer than the wetland background, and was reduced in temperature by passage through the adaptation zone. The time constants for adaptation (63% of change) were approximately one-half to 1 day. Soil temperatures followed a cyclic pattern, with decreasing amplitude with depth, and a time delay increasing with depth. The seasonal surface maximum was about 18 °C. The irrigation season started on May 1, with water at 10 °C, and ended in early October, with water at 10 °C. The soil conduction model was used to infer cyclic surface temperatures, with a smoothed result compared to synoptic temperature measurements in surface water. Background zone fitting parameters were the Julian day of surface maximum temperature (196), mean temperature (7.9 °C), surface amplitude (10.3 °C), and penetration depth (1.0 m). Soil heat fluxes were vertically downward during the warm season, and back up toward the surface with maxima of 1.4 MJ/m² d in the discharge zone. This vertical soil heat flux was of small importance to the summer energy budget, which was dominated by solar radiation and evaporative cooling.     

Wastewater treatment at the Houghton Lake wetland: Vegetation response

This paper describes the vegetation responses in a very long-running study of the capacity of a natural peatland to remove nutrients from treated wastewater. Data are here presented and analyzed from three decades of full-scale operation, during which large changes in the plant communities occurred. An average of 600,000 m³ year⁻¹ of treated wastewater was discharged seasonally (May 1–October 31) to the Porter Ranch peatland near the community of Houghton Lake, Michigan. This discharge was seasonal, commencing no sooner than May 1 and ending no later than October 31. During the winter half-year, treated wastewater was stored at the lagoon site. This water contained 3.5 mg/L of total phosphorus, and 7 mg/L of dissolved inorganic nitrogen (DIN). Nutrients were stored in the 100 ha irrigation area, which removed 94% of the phosphorus (53 metric tons) and 95% of the dissolved inorganic nitrogen. Phosphorus was stored in new biomass, increased soil sorption, and accretion of new soils and sediments, with accretion being dominant. The irrigation area underwent large changes in ecosystem structure, in which the original plant communities were displaced by Typha spp. There was an initial fertilizer response, characterized by much larger standing crops of vegetation, at about triple the crop in control areas. Increased biomass was accompanied by increases in tissue nitrogen and phosphorus content, by factors of two and three, respectively. The plant community shift, from the initial sedge-willow and leatherleaf-bog birch cover types to a cattail-dominant cover type, progressed to a 83-ha area over the 30-year period of record (POR). The interior portion of this new cattail patch became a floating mat. There were large gradients in stem densities and stem heights within the impacted area. The response times of the vegetative community shifts were on the order of 10 years for 63% of the final impact zone development. The grow-in time for development of a new larger standing crop in the discharge zone was also 10 years. The impacted area was stable at the 30-year time, without any further moving fronts. Around the cattail zone, there were fringe areas that contained a mixture of the original cover types intruded by relatively small amounts of cattail.     

Wastewater treatment at the Houghton lake wetland: Soils and sediments

This paper describes the sediment and soils responses in a very long-running study of the capacity of a natural peatland to remove nutrients from treated wastewater. Data are here presented and analyzed from three decades of full-scale operation (1978–2007), during which large changes in the wetland soils occurred. An average of 600,000 m³ y⁻¹ of treated water was discharged each warm season to the Porter Ranch peatland near the community of Houghton Lake, Michigan. This discharge was seasonal, commencing no sooner than May 1 and ending no later than October 31. During the winter half-year, treated wastewater was stored at the lagoon site. This water contained 3.5 mg/L of total phosphorus, and 7 mg/L of dissolved inorganic nitrogen. Nutrients were stored in the 100 ha irrigation area, which removed 94% of the phosphorus (53 t) and 95% of the dissolved inorganic nitrogen. Phosphorus was stored in new biomass, increased soil sorption, and accretion of new soils and sediments, with accretion being dominant. Peat probings, water level increases and topographical surveys established quantitative measures of soil accretion. Over 30 cm of new soil developed, in which nutrient storage occurred. Phosphorus concentrations in the new soil were approximately 2000 mg P/kg, and the nitrogen concentration was 2–3%DW. The removal of TSS was effective, but minor in comparison to the internal generation and cycling of produced particulates. Later in the project history, the interior portion of impacted area became a floating mat. Sedimentation processes then occurred with no exposure to above-mat detrital processes. Trace element analyses showed no appreciable accumulation of heavy metals, other than the calcium and iron that characterized the antecedent wetland and the incoming water. Biomass cycling models were found to produce reasonable estimates of the measured nutrient accumulations. The light loadings of nutrients to this system produced dramatic effects in the ecosystem, but were lower than the range seen in some other treatment wetlands. Insufficient nitrogen was added to support the new biomass, and nitrogen fixation was identified as a possible compensatory mechanism.     

Performance analysis of the Richland-Chambers treatment wetlands

The Tarrant Regional Water District (TRWD) is supplementing the flows to Richland-Chambers Reservoir, to meet future water supply needs of Dallas-Ft. Worth, TX. The Trinity River is the new source, but quality is not adequate. TRWD has constructed and investigated treatment wetland facilities located near the reservoir to upgrade river water quality, from an eight-year study at a 0.72 ha pilot site, and a five-year study at a 102 ha field-scale site. Both systems had a sedimentation basin followed by wetland cells in series. The pilot had two basins feeding three trains of three wetland cells each, while the field-scale system had one basin followed by four wetland cells in series. Water depths were about 30 cm for the pilot, and 40 cm for the field-scale. Design nominal detention times were roughly 5 and 9 days for pilot basins and wetland trains; and 1.5 and 8 days for the field-scale. The systems ran year-round, supplied with water pumped from the river, which at times was predominantly treated wastewater from the Dallas-Fort Worth metroplex. The primary target contaminants were suspended solids, nitrogen, and phosphorus. Nitrogen forms in pumped flows from the river were dominated by oxidized nitrogen, which was mostly nitrate nitrogen. Pilot nitrate removal from the river water was 92%, and 61% for phosphorus, while sediment removal was 97%. Field-scale nitrate removal from the river water was 77%, and 45% for phosphorus, while sediment removal was 96%. The field-scale project is located on land owned by the Texas Parks and Wildlife Department, and they participate in management of the wetlands for the secondary purpose of wildlife habitat.     

Hydrology and history: land use changes and ecological responses in an urban wetland

The impacts of changing land use on hydrology and dominant plant species from 1850–1990 were investigated in a palustrine wetland in southern Wisconsin, USA. Aerial photographs, historic maps and water levels of the area were used to determine changes in land use, wetland vegetation, and groundwater and surface flows over time. Piezometers and water table wells were monitored weekly for two years. Vegetation was quantified in four one-square meter quadrats at each water level measurement site. Linear regression models and multivariate ordinations were used to relate wetland plant species to hydrologic, chemical and spatial variables. The current hydrologic budget of the wetland was dominated by precipitation and evapotranspiration, although overland flow into the wetland from the subwatershed has increased twenty-fold since 1850. Water level stabilization in the adjacent Yahara River, creek channelization, and groundwater pumping have decreased inputs of groundwater and spring-fed surface water, and increased retention of precipitation. Typha spp. and Phalaris arundinacea L. have increased in the wetland, while Carex spp. have decreased. Phalaris arundinacea was found most often in the driest sites, and the sites with the greatest range of water levels. Typha spp. dominated in several hydrologic settings, indicating that water depth was not the only factor controlling its distribution. The distributions of dominant plant species in the wetland were most closely correlated with site elevation and average water levels, with some weaker correlations with vertical groundwater inflows and specific conductance.     

Critical source area controls on water quality in an agricultural watershed located in the Chesapeake Basin

The importance of agricultural land use activities for supplying nutrients (N, P) to the Chesapeake Bay is examined and nutrient sources for a typical agricultural hill-land watershed within the Chesapeake Basin are identified and assessed. Based on up to 30 years of experimental and monitoring data, the outflow, N, and P exported from this Pennsylvania watershed is examined in terms of critical source areas. Most of the surface runoff and P export occurs from areas near the stream. About 90% of the algal-available P exported in outflow was generated during the largest 7 storms/year. In contrast, nearly all the nitrate (NO₃) exported originated as subsurface flow entering the soil or ground water some distance from the stream, and mostly occurred during nonstorm flow periods. The NO₃ export observed over the long term corresponds to the N excess computed by N balance obtained by farmer survey for agricultural land. By combining land use, hydrologic processes, watershed position, soil P status, and N balance information for agricultural land, the major source areas for P and N are predictable and identifiable. We apply these ideas and techniques to our research watershed and present the results as an example of this approach.     

Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO₂⁻ + NO₃⁻)-N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year⁻¹ and 1.1 cm year⁻¹, respectively. Sediment retention totaled nearly 500 MT year⁻¹.     

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (D_b), total carbon (C_t), nitrogen (N_t), and phosphorus (P_t), extractable phosphate (PO_4w), nitrogen (N_ex), and cations (Ca_ex, Mg_ex, K_ex, Na_ex), as well as pH. Bulk density, P_t, Ca_ex, Mg_ex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.     

Investigating the effects of point source and nonpoint source pollution on the water quality of the East River (Dongjiang) in South China

Understanding the physical processes of point source (PS) and nonpoint source (NPS) pollution is critical to evaluate river water quality and identify major pollutant sources in a watershed. In this study, we used the physically-based hydrological/water quality model, Soil and Water Assessment Tool, to investigate the influence of PS and NPS pollution on the water quality of the East River (Dongjiang in Chinese) in southern China. Our results indicate that NPS pollution was the dominant contribution (>94%) to nutrient loads except for mineral phosphorus (50%). A comprehensive Water Quality Index (WQI) computed using eight key water quality variables demonstrates that water quality is better upstream than downstream despite the higher level of ammonium nitrogen found in upstream waters. Also, the temporal (seasonal) and spatial distributions of nutrient loads clearly indicate the critical time period (from late dry season to early wet season) and pollution source areas within the basin (middle and downstream agricultural lands), which resource managers can use to accomplish substantial reduction of NPS pollutant loadings. Overall, this study helps our understanding of the relationship between human activities and pollutant loads and further contributes to decision support for local watershed managers to protect water quality in this region. In particular, the methods presented such as integrating WQI with watershed modeling and identifying the critical time period and pollutions source areas can be valuable for other researchers worldwide.     

Phosphorus budgets in Everglades wetland ecosystems: the effects of hydrology and nutrient enrichment

The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough (‘Slough’), shallower water oligotrophic Cladium jamaicense (‘Cladium’), partially enriched C. jamaicense/Typha spp. mixture (‘Cladium/Typha’), and enriched Typha spp. (‘Typha’) marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m⁻² yr⁻¹ in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m⁻² yr⁻¹ in partially enriched Cladium/Typha, and 1.6 g P m⁻² yr⁻¹ in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface waters in P-enriched areas of the Everglades.     

Influence of hydropattern and vegetation type on phosphorus dynamics in flow-through wetland treatment systems

Phosphorus (P) flux from wetland soil can be a significant factor affecting overall wetland treatment performance. The purpose of our study was to quantify the effects of water level drawdown on P exchange between surface water and organic soil in a constructed wetland. We used 12 fiberglass mesocosms filled with 30 cm of peat soil to quantify nutrient exchange between surface water and organic soil in a wet-dry-wet cycle. Six mesocosms were planted with emergent macrophytes and six mesocosms were maintained free of emergent vegetation. We evaluated four treatments including continuously and intermittently flooded treatments, both with and without emergent macrophytes. Each treatment was replicated three times and every mesocosm was plumbed to monitor flow volumes and water chemistry. Effluent P concentrations were similar for all four treatments prior to first drawdown period. However, upon re-flooding, all intermittently flooded tanks exhibited a three to fourfold increase in surface water P concentration, which lasted for a period of up to ten weeks. The magnitude of nutrient flux to surface water and the time period over which P release took place were season dependent, with longer duration of high nutrient flux during dry-season drawdowns. Results of repeated measures analysis indicated that hydropattern was the dominant factor affecting P-flux to overlying surface water, while presence or absence of emergent vegetation had no significant influence on effluent concentrations. Organic and particulate phosphorus fluxes were substantially higher in treatments lacking emergent macrophytes, subsequent to the dry-season drawdowns. Intermittently flooded treatments with no emergent vegetation generated the most dissolved and particulate phosphorus. Our results indicate that maintaining saturated soil is sufficient to retain stored P, while plants played no significant role in P retention for a wetland receiving P-loading rate on the order of 0.1 g week⁻¹ during a wet-dry-wet cycle.     

Surface water quality and information about the environment surrounding Inle Lake in Myanmar

Inle Lake is the second largest lake in Myanmar and one of the nine key sites for sightseeing there. An analysis of its water quality has not been published before. The objective of this study is to reveal the current situation and find any major problems with the lake. For this purpose, the natural and cultural environments were examined. Some physical and chemical aspects of the surface water were assayed in situ for 2 days in November 2004. The principal ions were analyzed in our laboratory. The main cation and anion species in the lake surface water are Ca²⁺ and HCO₃ ⁻. Its high calcium content can be attributed to the limestone of Shan Plateau around the lake. The alkalinity of the lake water was 3829–4114 acid-neutralizing capacity (ANC) (pH 7.8–8.0); it can be attenuated by Ca²⁺. The concentrations of PO₄-P, NO₂-N, and NO₃-N were relatively high; these could originate from domestic and agriculture uses. The trophic state is eutropic. The concentrations of coliform bacteria indicated that the lake water was unfit to drink, but some people use it for drinking anyway. The bacteria could enter the lake through the direct latrine system used there. The thermal type of the lake is presumed to be warm polymictic. More extensive studies are needed because the lake is thought to be the most changing site in Myanmar as a result of both the tourism boom and increasing agricultural activity.     

Relationships between wetland ecotones and inshore water quality in the Ugandan coast of Lake Victoria

Much of the lake shore in Lake Victoria is covered by extensive wetlands, often dominated by dense papyrus stands that extend out over the lake waters. These wetlands, their extension and management play a role in the physical, chemical and biological conditions of the inshore waters. Continuous transects along 180 km of shoreline together with spatial grids of sampling sites in eight bays were performed in the Ugandan inshore waters in order to analyze the relationships between the wetland characteristics and water quality. Measurements of extension of the wetland ecotones, water temperature (T), pH, Secchi disk depth (SD), dissolved oxygen (DO), total nitrogen (TN), total phosphorous (TP), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and chlorophyll-a (CHL) were made in each sampling area. Data of T, pH and DO collected during the transects showed that the water characteristics of the bays differ from the open shoreline. Moreover, the magnitude of these physical–chemical differences is strongly conditioned by the dimension of the bordering wetlands. Bays with extensive wetlands ecotones were characterized by cooler, more acidic and poorly oxygenated waters. TN : TP ratios and especially DIN : SRP ratios decreased with the wetland presence along the coastline, showing a higher probability of N limitation in the inshore waters where large wetlands are present. Results point to denitrification processes in the wetland ecotones as the cause of this trend. The distribution of CHL was found to be highest in the presence of two significant point loading sources: a river (in Katonga Bay) and a major population centre (Kampala, in Murchison Bay). The reduction of external P loading is shown as an important step in the management of the eutrophication process of Lake Victoria inshore waters.     

Waste treatment and biogas quality in small-scale agricultural digesters

Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2968 mg/L to 472 mg/L) and higher dissolved nutrient concentration (NH₄-N increased by 78.3% to 82.2 mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH₄-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater.     

Influence of draining on soil phosphorus forms and distribution in a constructed wetland

Seasonal water-table fluctuations in wetlands can result in flooded and drained conditions in the surface soil. In constructed wetlands water level drawdown and soil drainage are used in management to consolidate detrital materials, accelerate soil build up, and provide easy access for other management operations. A greenhouse study was conducted using intact peat soil cores to evaluate the changes in bioavailable P and other fractions following draining and reflooding. Measurements of floodwater dissolved reactive P (DRP) indicated that draining and soil exposure could result in large P flux to the overlying water column. Phosphorus flux in soils drained for 6 weeks was 10-fold higher (334 mg P m⁻² day⁻¹) than in soils drained for 3 weeks (33 mg P m⁻² day⁻¹). Soil exposure also resulted in an increase in bioavailable inorganic P (estimated by KCl extraction) at the expense of labile organic P pool. The KCl-P pool, which was initially less than 2% of total P (TP), increased to 3% and 13% of TP after 3 and 6 weeks draining, respectively. Results suggest that various soil P fractions, particularly those in newly accreted materials, were highly unstable and could be released in a more available form when newly accreted soils undergo drying. Water level drawdown and reflooding could result in significant P release, a possible stimulation of algal blooms and other water quality problems. Therefore, soil characteristics and chemistry and their impact on water quality should be a major consideration when one adopts the flood-drain technique in wetland management.     

Characteristics of fluctuations in salinity and water quality in brackish Lake Obuchi

Fluctuations in the salinity and physicochemical characteristics of water quality were surveyed in brackish Lake Obuchi on the Shimokita Peninsula in Aomori, Japan. The mean salinity in the surface layer in all regions of Lake Obuchi was about 10 psu, whereas in the basin region at depths of greater than 3 m it was 20 psu. Furthermore, all the year round the halocline was formed at depths of 1–4 m. The maximum density gradient along a vertical axis in the center of the lake was observed at depths of 1–2 m in summer and 2–4 m in spring and fall. The depth of the maximum density gradient fluctuated with the seasons. In summer the water in the bottom layer was anoxic, and Fe, Mn, PO₄ ³⁻-P, and NH₄ ⁺-N supplied from the bottom sediment accumulated at high concentrations below the halocline. Thus, it was observed that the transfer of substances between the layers above and below the barrier formed by the halocline is suppressed. Although Lake Obuchi is small and shallow, the inflowing seawater easily resides, and a stable halocline readily forms because of the shape of its basin, which suddenly deepens on the Pacific Ocean side. Received: May 24, 1999 / Accepted: September 25, 1999     

Comparison between biological and chemical treatment of wastewater containing nitrogen and phosphorus

The present work compared chemical and biological treatment methods to achieve the most efficient treatment for the reduction or elimination of phosphorus and nitrogen from mixed industrial–domestic wastewaters. Batch chemical precipitation by ferric chloride and aluminum sulfate (alum) and a continuous biological suspended growth system were investigated as well as the optimum operating conditions. Concerning chemical treatment, Alum generally achieved a higher removal efficiency percentage for the investigated pollutants compared with FeCl₃ at their optimum pH and dose, especially with chemical oxygen demand (COD). FeCl₃ treatment achieved success only with phosphorus removal, while none of the COD, 5-day biochemical oxygen demand (BOD₅), total nitrogen (TN) and N–NH₃ achieved acceptable treatment and remained above the maximum permissible limits (MPL). Thus, for such wastewaters, alum is more efficient than FeCl₃. Biological treatment exhibited higher efficiencies, particularly towards nitrogen. TN removal increased by increasing the flow rate to 30–60 l/day. N–NH₃ removal was effective at the slowest flow rate and decreased with increasing flow rate, while an opposite trend was recorded for N–NO₃. At all flow rates, phosphorus levels were below the accepted MPL for discharging into natural systems. Moreover, there was a general trend for the proposed biological treatment to achieve a high removal efficiency for BOD₅ and COD, bringing them to acceptable levels to be released into watercourses safely, especially at the slowest flow rates. Thus, integration between the proposed chemical and biological treatment is highly recommended, producing high-quality effluents acceptable by the environmental law.     

Application of modified water quality indices as indicators to assess the spatial and temporal trends of water quality in the Dongjiang River

The Dongjiang River plays an important role in southern China, as a source for irrigation and potable water of Hongkong and the other parts of the Pearl River Delta (PRD). The water quality index (WQI) was calculated to assess the spatial and temporal variability and identify the classification of water quality in the river. In order to simplify the procedure and reduce the analytical costs of the water quality evaluation, a modified WQI (defined as WQI_min) was introduced based on Principal Component Analysis (PCA) and correlations analyses of the water parameters detected in dry and wet seasons during 2011–2012. Compared with the previous index, similar spatial changing trend and classification of the water quality were obtained by WQI_min, which was composed of pH, temperature, total suspended solid, NH₄⁺-N, and NO₃⁻-N. The results showed an excellent water quality in the tributary site near the reservoir, a good water quality in the upstream of the river, and medium water quality in the downstream of the river, which suggested that the urban wastewater originated from increasing population size and industry development in the downstream mainly led to the deterioration of water quality along the river. Moreover, WQI_min could more adequately reflect the seasonal changes of water quality which was slightly worse in dry season than wet season. Our results also suggest that continuous monitoring should be conducted to prevent pollution from industry and anthropogenic activities.     

洞庭湖底栖动物种类分布及水质生物学评价

1 995年枯水、平水、丰水期对洞庭湖设 6个断面进行采样 ,共采到底栖动物 58种 ;其密度变幅为 78～ 544 .5个 /m2 ;1 0种常见种均成聚集分布。采用综合生物污染指数评价水体质量 ,结果显示洞庭湖整体水质受到轻度污染 ,评价结果与化学污染指数评价结果一致 ;各采样断面综合生物污染指数均明显大于 1 981～ 1 982年的测量结果 ,表明水体质量变差     

Association between phosphorus and suspended solids in an Everglades treatment wetland dominated by submersed aquatic vegetation

Restoration of the Everglades requires reduction of total phosphorus (TP) in the influent run-off from the Everglades agricultural area (EAA). The Everglades nutrient removal project tested phosphorus (P) - removal efficiencies of several treatment wetland cells. The best TP reduction has occurred within the submersed aquatic vegetation (SAV) - dominated treatment Cell 4. A significant proportion of the P reduction in Cell 4 over several years has been in the form of particulate P (PP). This study was conducted to (i) determine and compare the components of suspended solids in the Cell 4 influent and effluent waters, and (ii) investigate associations between PP and individual particulate components. Identification and quantification of components were accomplished using X-ray diffraction, thermogravimetry, scanning electron microscopy, and energy dispersive X-ray elemental analysis. The dominant particulate components in the Cell 4 water column are organic matter (OM), biogenic Si (predominantly diatom frustules), and calcite. Concentrations of PP, suspended solids, and particulate OM were greater at the Cell 4 inflow than at the outflow; consistent differences between particulate calcite in the influent vs. the effluent were not found. PP was positively correlated with particulate OM, but was not correlated with calcite. Data suggest that particulate OM, including microbial cells, plays an important role in P transport from the EAA. Possibly, a shift from planktonic to periphytic microbial distribution contributes to PP reduction. The importance of planktonic organisms as vectors of P in Everglades water warrants further study.