Effects of River Impoundment on Ecosystem Services of Large Tropical Rivers: Embodied Energy and Market Value of Artisanal Fisheries

Abstract:  Applying the ecosystem services concept to conservation initiatives or in managing ecosystem services requires understanding how environmental impacts affect the ecology of key species or functional groups providing the services. We examined effects of river impoundments, one of the leading threats to freshwater biodiversity, on an important ecosystem service provided by large tropical rivers (i.e., artisanal fisheries). The societal and economic importance of this ecosystem service in developing countries may provide leverage to advance conservation agendas where future impoundments are being considered. We assessed impoundment effects on the energetic costs of fisheries production (embodied energy) and commercial market value of the artisanal fishery of the Paraná River, Brazil, before and after formation of Itaipu Reservoir. High-value migratory species that dominated the fishery before the impoundment was built constituted a minor component of the contemporary fishery that is based heavily on reservoir-adapted introduced species. Cascading effects of river impoundment resulted in a mismatch between embodied energy and market value: energetic costs of fisheries production increased, whereas market value decreased. This was partially attributable to changes in species functional composition but also strongly linked to species identities that affected market value as a result of consumer preferences even when species were functionally similar. Similar trends are expected in other large tropical rivers following impoundment. In addition to identifying consequences of a common anthropogenic impact on an important ecosystem service, our assessment provides insight into the sustainability of fisheries production in tropical rivers and priorities for regional biodiversity conservation .     

PRIMARY PRODUCTIVITY AND PLANKTON COMMUNITIES IN A TWO-RESERVOIR SERIES1

ABSTRACT: It is suggested that new impoundments undergo an initial period of trophic upsurge lasting one to three years because of organic detritus and inorganic nutrients from the inundated basin. The new Monksville Reservoir in Passaic County, New Jersey, provided an opportunity to study the accelerated transformation of the Wanaque River into a 200-ha lake and to compare productivity with the older Wanaque Reservoir located immediately downstream. A one-year investigation of both reservoirs was conducted during 1988. The primary productivity (0.547 g C m^?2 d^?1) of the new Monksville Reservoir was not significantly different from that of the established Wanaque Reservoir (0.668 g C m^?2 d^?1). Mean surface chlorophyll a concentrations were similar (3.0–4.0 μg 1^?1), although the Monksville Reservoir exhibited more pronounced chlorophyll peaks in spring and late autumn. Phytoplankton and zooplankton populations were consistently larger and fluctuated sharply in the Monksville Reservoir. Both reservoirs became thermally stratified, but only the Monksville Reservoir developed a metalimnetic dissolved oxygen minimum. The results demonstrated that the predicted trophic upsurge in the new reservoir did not occur in the first year therefore, the ecosystem dynamics did not fit the model for larger reservoirs.     

PARTIAL AREA RESPONSE ON SMALL SEMIARID WATERSHEDS1

ABSTRACT: Significant errors in estimating surface runoff and erosion rates are possible if a watershed is assumed to contribute runoff uniformly over the entire area, when actually only a portion of the entire area may be contributing. Generation of overland flow on portions of small semiarid watersheds was analyzed by three methods: an average loss rate procedure, a lumped-linear model, and a distributed-nonlinear model. These methods suggested that, on the average, 45, 60, and 50% of the drainage area was contributing runoff at the watershed outlet. Infiltrometer data support the partial area concept and indicate that the low infiltration zones are the runoff source areas as simulated with the distributed-nonlinear model.     

INPUT/OUTPUT MODELS AS DECISION AIDS FOR LAKE RESTORATION1

ABSTRACT: Over the past several years, input/output models have been used increasingly as decisionmaking aids in the design of lake restoration activities because they provide an approximation of the link between nutrient influx and lake trophic status. To evaluate the applicability of these models as design tools, a study was conducted in which “before” and “after” data were obtained for 25 lakes which experienced reductions in nutrient inflow, and comparisons were made of observed and predicted changes in lake conditions. Three input/output models were used as predictive tools to describe lake response: those reported by Dillon and Rigler (1974) and by Vollenweider (1975, 1976). Based on described trophic states of oligotrophic, mesotrophic, and eutrophic, it was found that all three models yielded accurate predictions for at least 70 percent of the study lakes. The model of Vollenweider (1976) performed slightly better than the other two (80 percent correct) on the data set studied.     

Experimental Study of Gas-Liquid Interfacial Properties in a Stepped Cascade Flow

Gas-liquid interface measurements were conducted in a strongly turbulent free-surface flow (i.e., stepped cascade). Local void fractions, bubble count rates, bubble size distributions and gas-liquid interface areas were measured simultaneously in the air-water flow region using resistivity probes. The results highlight the air-water mass transfer potential of a stepped cascade with measured specific interface area over 650 m^–1 and depth-average specific area up to 310 m^–1. A comparison between single-tip and double-tip resistivity probes suggests that simple robust single-tip probes may provide accurate, although conservative, gas-liquid interfacial properties. The latter device may be used in the field and in prototype plants. Notation a = specific interface area (m^–1); a _mean = depth-average specific interface area (m^–1): a _mean=frac1Y ₉₀limits sup> Y ₉₀ sup ₀(1–C)dy; C = local void fraction; C _gas = dissolved gas concentration (kg m^–3); C _mean = depth-average mean air concentration defined as: C _mean=1–d/Y ₉₀; C _s = saturation concentration (kg m^–3); D = dimensionless air bubble diffusivity (defined by [1]); d = equivalent clear-water flow depth (m): d=limits sup> Y ₉₀ sup ₀(1–C) dy; d_ab = air bubble diameter (m); d_c = critical flow depth (m); for a rectangular channel: d _c=sqrt[3]q _w ²/g; F = air bubble count rate (Hz); F _max = maximum bubble count rate (Hz), often observed for C=50%; g = gravity acceleration (m s^–2); h = step height (m); K _L = liquid film coefficient (m s^–1); K = integration constant defined as: K=tanh ^–1 sqrt0.1)+(2D)^–1 [1]; L = chute length (m); N = velocity distribution exponent; ———– ^*Corresponding author, E-mail: h.chanson@mailbox.uq.edu.au Q _w = water discharge (m³ s^–1); q _w = water discharge per unit width m² s^–1); t = time (s); V = local velocity (m s^–1); V _c = critical flow velocity (m s^–1); for a rectangular channel: V _c=sqrt[3]q _w g V _max = maximum air-water velocity (m s^–1); V ₉₀ = characteristic air-water velocity (m s^–1) where C = 90%; W = channel width (m); x = longitudinal distance (m) measured along the flow direction (i.e., parallel to the pseudo-bottom formed by the step edges); y = distance (m) normal to the pseudo-bottom formed by the step edges; Y₉₀ = characteristic distance (m) where C=0.90; Y ₉₈ = characteristic distance (m) where C=0.98; = slope of pseudo-bottom by the step edges; = diameter (m).     

Great Lakes monitoring results--comparison of probability based and deterministic sampling grids

The Great Lakes may be viewed as a coastal environment, affected by the same meteorological and physical forces as the coastal ocean. The U.S. EPA, Great Lakes National Program Office (GLNPO) has monitored the open waters of the lakes, annually, since 1983. As part of the U.S. EPA Environmental Monitoring and Assessment Program (EMAP), a pilot study was performed in Lake Michigan to compare the existing GLNPO deterministic sampling grid with the EMAP probabilistic grid. Results of chemical analyses of trophic status indicators (total phosphorus and chlorophyll a) as well as nutrients and conventional limnological measurements, from spring and summer surveys in 1992 indicate little difference between the grids in the offshore region of the lake. The few statistically significant differences may be due to station distribution throughout the lake, or simple chance. This might be expected due to the well mixed nature of the open waters of Lake Michigan. The detection of a long-term trend for total phosphorus in Lake Michigan benefits from an annual program: viewing cumulative frequency distributions based on a four year EMAP interval does not convey information on the decrease in phosphorus in the lake. If the EMAP sampling grid were to be used in the Great Lakes, pilots in each of the lakes would be necessary for utilization of the existing long-term record as a basis for trend detection.     

The algal community as an indicator of the trophic status of Lake Patzcuaro, Mexico

An evaluation of water quality and phytoplankton composition position was carried out in order to determine the trophic conditions of Lake Patzcuaro (2035 m above sea level), a high altitude tropical lake. Temperatures ranged from 15 to 23 degrees C. Total phosphorus and inorganic nitrogen showed a seasonal variation; highest values coincided with the rainy season (0.48 and 2.1 mg litre(-1), respectively). Dissolved oxygen ranged from 2 to 7.9 mg litre(-1) at the surface and from 0.6 to 7.3 mg litre(-1) on the bottom, the lowest values being found in shallow zones. Average transparency varied from 0.62 to 1.4 m Secchi depth. Rainfall was a primary factor in seasonal variability as it influenced both physical and biological conditions by contributing to the transport and deposition of silt, which mixed with sinking algal cells. The composition of the surface phytoplankton segregated along five major divisions comprising a total of 49 species. General seasonal patterns of dominance alternated in a sequence beginning with Bacillariophyta, through Chlorophyta to Cyanophyta. Diatoms, the dominant group from February to early June, included Melosira granulata, Stephanodiscus sp., Synedra sp. and Fragilaria sp. During the rainy season (late June to September), Microcystis aeruginosa, Oscillatoria sp., Anabaena sp., Merismopedia sp., Crucigenia cuadrata, Oocystis lacustris, Selenastrum gracile, Mallomonas sp. and Tetraediella sp. were important. Melosira granulata was present throughout the period of study. Spatial and temporal variability in both physical and biological conditions make it difficult to assign a specific trophic state to Lake Patzcuaro. Nevertheless, analysis of the algal community indicates a generally mesotrophic condition.     

“十一五”期间滴水湖富营养化评价

采用综合营养状态指数TLI(Σ)对"十一五"期间滴水湖富营养化状态、时空分布特征及变化趋势进行了评价及分析。结果表明:滴水湖水质整体处于轻度富营养状态,石皮泐港进水口的综合营养状态指数大于湖区各点位;每年4月-5月和8月-10月两个时间段,滴水湖综合营养状态指数较高;"十一五"期间,滴水湖的富营养化状态呈现不显著下降的趋势。建议加强对水体叶绿素a浓度等生物指标的监测,以更全面地评价滴水湖的营养状态。     

多点交替进水阶式A2/O工艺强化脱氮除磷

为强化CMICAO(多点交替进水阶式A2/O)工艺的脱氮除磷性能,通过调整进水C/N〔ρ(COD_Cr)/ρ(TN)〕、进水端厌氧池和缺氧池的进水流量比对CMICAO工艺参数进行优化,考察其对氮、磷去除的影响. 结果表明:试验条件下,C/N的提高可增强SND(同步硝化反硝化)作用,氮的去除效果也随之提高,C/N≥7时,前好氧池同步硝化反硝化率达到61%,出水ρ(TN)≤9.0 mg/L;在相同工况下,较低的C/N下反硝化除磷现象更明显. 综合考虑,C/N在5~7范围内,可取得较好的整体脱氮除磷效果. 优化工艺进水碳源分配可提高碳源利用效率,氮、磷的去除效果受进水流量比的影响较大,当厌氧池和缺氧池进水流量比为2.0时,可强化缺氧池的反硝化除磷作用,TN和TP去除率分别为75%和92%,出水ρ(COD_Cr)、ρ(NH+₄-N)、ρ(TN)和ρ(TP)分别为28.7、1.9、9.2和0.27 mg/L,通过优化实现了CMICAO工艺对氮、磷去除的强化.      

Least-inference methods for constructing networks of trophic flows

The construction of material and energy budgets within ecosystems has long been accomplished via manual calculation. Recently, optimization techniques have been adapted to automate the procedure, but these methods require assumptions that may not square with biological reality. Two algorithms are developed to construct ecosystem budgets under minimal inference. Although the methods do not recapitulate the model used to generate the input data, analysis reveals that the results do not differ statistically from networks that were constructed manually.