Variability in stock assessment of cockles (Cerastoderma edule L.) in the Oosterschelde (in 1980–1990), in relation to environmental factors

The edible cockle (Cerastoderma edule L.) is a dominant suspension feeder in the Oosterschelde, a 351 km² tidal bay in the SW Netherlands. To establish its role in the benthic foodweb, and to assess the impact of human activities, data on density, age composition, biomass and growth were collected from several tidal flats in the Oosterschelde between 1980 and 1990.To estimate the overall biomass development of the cockle, a simple model was used, in which three growing seasons are defined for the cockle population. A standard individual growth curve was constructed. A negative exponential mortality function was assumed to estimate the number of recruits. By combining the estimated number of recruits, the estimated specific mortality rate and the standard individual growth curve, numbers and biomass of each age group in the Oosterschelde population were estimated. Average biomass (including shell organics) per m² of tidal flat in August varied from 140 g AFDW in 1980 to 21 g AFDW in 1989, implying a total cockle stock on all tidal flats of 19 170 to 2350 tonnes AFDW (72 × 10³ to 9 × 10³ tonnes flesh), respectively.A comparison of results from field surveys and the reconstructed stock estimations showed large deviations. However, an uncertainty analysis performed on the model showed that most field data fitted within the minimum and maximum biomass calculated.Total biomass is largely dependent on the strength of certain year classes. In this respect, the year classes 1979, 1982, and 1985 were good. Effects of the construction of the storm-surge barrier and the compartmentalisation dams could not be demonstrated.The year-to-year variation in cockle stocks, assessed in the way described in this paper should be regarded as relative, because a systematic survey of the intertidal flats was not performed every year, but population dynamics from selected stations were used instead.     

The mobile epifauna of the soft bottoms in the subtidal Oosterschelde estuary: structure,function and impact of the storm-surge barrier

Data on the mobile epifauna of the Oosterschelde estuary, collected by beam trawl, were compiled from several studies. Multivariate statistical techniques brought out the fact that the Oosterschelde, when compared with neighbouring areas, has a characteristic epibenthic fauna. Diversity as measured by Hill's diversity numbers N through N ₊ , is higher for the Oosterschelde (N₁ = 4.5) than for the Voordelta (N₁ = 3.5) and the Westerschelde (N₁ = 2.2).Four epifaunal communities can be distinguished within the Oosterschelde, the two most seaward communities being the richest. Annual production is estimated at about 6 gADW m^–2 yr^–1, annual consumption is estimated at over 25 gADW m^–2 yr^–1. These results are highly dependent on the assumptions. Over 85% of the epibenthic production and consumption in the Oosterschelde is accounted for by only six species: starfish Asterias rubens, plaice Pleuronectes platessa, bib Trisopterus luscus, brown shrimp Crangon crangon, shore crab Carcinus maenas and dab Limanda limanda. In spite of its abundance, the sand goby Pomatoschistus minutus contributes little to the production.From the available data it is difficult to assess the impact of the construction of the storm-surge barrier and the compartmentalization dams on the epibenthic fauna. The increase in flatfish in the Hammen area is probably linked to the decrease in current velocities in that area. On the other hand the increase in the gadoids bib and whiting Merlangius merlangus is predominantly due to the stronger year classes in the post-barrier time period. Lower nutrient inputs through the Northern branch, in combination with the increase of the gadoids, may have caused the decline of the brown shrimp in the Oosterschelde. A decrease has also been observed in the sandeel Ammodytes tobianus and the hooknose Agonus cataphractus.     

Application of frequency ratio and logistic regression models for assessing physical wetland vulnerability in Punarbhaba river basin of Indo-Bangladesh

Growingly scarce ecologically viable flood plain wetland of the Punarbhaba river basin is further endangered due to flow modification through Komardanga dam. This work intends to discover physical vulnerability of the wetlands in Punarbhaba river basin of Indo-Bangladesh considering seven conditioning parameters, e.g., water presence frequency (WPF) map, flood inundation map, frequency of pixel being non-permanent, agriculture presence frequency (APF) map, fragmentation of wetland, normalized differentiation built up index (NDBI), and wetland changes (WC). Frequency Ratio and Logistic Regression models have been used for deriving the vulnerability of wetland for both pre (1988–1992) and post dam (1993–2016) periods. From computed FR models it is exhibited that out of the total wetland area (194.81 km²), 5.88% and 2.92% area are high and very highly vulnerable in pre-dam period but such vulnerable area is increased to 33.45% and 23.10% in post-dam state (total wetland: 126.11 km²). LR models also state that in pre-dam period, high and very high vulnerable wetland area were 5.02% and 3.82% (total wetland: 194.79 km²) and it is enhanced to 28.94% and 24.49% in post-dam state (total wetland: 126.11 km²). Extensions of agricultural land, squeezing of active flood plain, lowering flood frequency are dominant determinants for growing wetland vulnerability.     

Changes in the waterbird populations of the Oosterschelde (SW Netherlands) as a result of large-scale coastal engineering works

Between 1982 and 1987, the construction of a storm-surge barrier and two secondary dams in the eastern and northern parts of the Oosterschelde/Krammer-Volkerak area resulted in the loss of 33% of the 170 km² of intertidal area in the estuary. Consequences for non-breeding waterbirds were evaluated on the basis of monthly high-tide counts during five seasons before and three seasons after the construction period.In the entire Oosterschelde/Krammer-Volkerak area, numbers of wintering waders decreased but those of ducks increased. Peak numbers and total number of bird-days changed little, but the seasonal pattern shifted from a midwinter maximum to a peak in autumn.In the Oosterschelde (excluding the Krammer-Volkerak), where 17% of the tidal flats disappeared, species feeding mainly on open water remained stable or increased. Species dependent on intertidal areas for foraging (mainly waders and dabbling ducks) generally decreased. Total density of intertidal foragers decreased slightly. In most intertidal species, the Oosterschelde wintering population showed a stronger decrease, or smaller increase, than was shown during the same period by numbers in Britain and Ireland which were taken as an index of the total W-European winter populations. Changes varied considerably between species, and were correlated with their distribution within the estuary. Species concentrated in the eastern sector, where most habitat loss occurred, declined more than species with a more westerly distribution.Results indicate that intertidal foragers forced to move from the enclosed parts of the estuary were not generally able to settle into the remaining intertidal areas. Both dispersal to adjacent areas (mainly by dabbling ducks) and mortality during severe winter weather (in some wader species) may have contributed to the declines. Populations of intertidal foragers apparently were (and consequently still are) close to carrying capacity, and further changes in capacity, as foreseen from geomorphological changes still under way in the estuary, are likely to be reflected in bird populations.Numbers of waders moulting in the Oosterschelde in late summer declined strongly compared to numbers in other seasons. Increased disturbance due to recreational activities may have played a role during this time of the year.     

Punching above their weight: Large release of greenhouse gases from small agricultural dams

Freshwater ecosystems play a major role in global carbon cycling through the breakdown of organic material and release of greenhouse gases (GHGs). Carbon dioxide (CO₂) and methane (CH₄) emissions from lakes, wetlands, reservoirs and small natural ponds have been well studied, however, the GHG emissions of highly abundant, small‐scale (<0.01 km²) agricultural dams (small stream and run‐off impoundments) are still unknown. Here, we measured the diffusive CO₂ and CH₄ flux of 77 small agricultural dams within south‐east Australia. The GHG emissions from these waterbodies, which are currently unaccounted for in GHG inventories, amounted to 11.12 ± 2.59 g CO₂‐equivalent m²/day, a value 3.43 times higher than temperate reservoir emissions. Upscaling these results to the entire state of Victoria, Australia, resulted in a farm dam CO₂‐equivalent/day emission rate of 4,853 tons, 3.1 times higher than state‐wide reservoir emissions in spite of farm dams covering only 0.94 times the comparative area. We also show that CO₂ and CH₄ emission rates were both significantly positively correlated with dissolved nitrate concentrations, and significantly higher in livestock rearing farm dams when compared to cropping farm dams. The results from this study demonstrate that small agricultural farm dams can be a major source of greenhouse gas emissions, thereby justifying their inclusion in global carbon budgets.     

Microphytobenthos in the Oosterschelde estuary (The Netherlands), 1981–1990; consequences of a changed tidal regime

During the period 1981–1990 the functioning of microphytobenthos in the carbon cycle was studied in the Oosterschelde, a mesotidal, euhaline estuary (SW Netherlands), both before and after completion of a storm-surge barrier in the sea ward entrance of the estuary in 1986, which reduced the tidal range to 88% and current velocities to 70% of their former values on average.The annual biomass cycle has changed from small spring and autumn peaks into a much larger summer peak. The average biomass during summer has increased from 70 to 170 mg Chlorophyll-a m². The average annual biomass has increased from 115 to 195 mg Chlorophyll-a m². As a consequence the (calculated) primary production by microphytobenthos has increased also, from 150 to 242 gC m^–2 y^–1 (14 045 to 22 265 tonnes C y^–1), and its share in the total primary production of the Oosterschelde has increased from 16 to 30%. These increases in biomass and primary production are mainly ascribed to a decrease in the dynamic forces (water current velocities) over the intertidal flats in most parts of the basin. Increased water transparency in parts of the estuary and increased import of inorganic carbon from the water column towards shoals may have contributed as well.The rate of reworking of the top layer of the soil (0–10 cm) has not changed significantly, as the decrease in Chlorophyll-a biomass with depth has hardly changed.     

Changes in the fish fauna of the Oosterschelde estuary — a ten-year time series of fyke catches

Frequency of occurrence of fish species was monitored on a fortnightly basis in four fykes and a weir in the Oosterschelde estuary from 1979 through 1988. This was done in order to record changes in the fish fauna that may have occurred as a response to the construction of a storm-surge barrier in the mouth of the Oosterschelde (1984–1986) and the concomitant building of compartmentalization dams in the landward part. These compartmentalization dams reduced the freshwater inflow into the system. Principal component analysis using the annual averages in frequency of occurrence suggests a slight shift occurred in the fish community separating a cluster of years 1979–1984 from the cluster 1985–1988. Many of the changes in individual species could be attributed to fluctuations in yearclass strength or were part of changes occurring on a wider geographical scale. The only impact of the construction works seems to be the decrease in a number of anadromous fish. Fish traps seem to be useful as a monitoring tool for a number of species. The value of the data collected could be improved if catch size and length-frequency data are recorded.     

Overwintering waterfowl on Swiss lakes: how are abundance and species richness influenced by trophic status and lake morphology?

During the period 1980–1990 long-term physical, chemical and ecological studies were carried out, to study the changes induced by the building of a storm-surge barrier in the mouth of the Oosterschelde estuary and two large auxiliary compartment dams in the rear ends of the estuary. The storm-surge barrier was constructed in the mouth of Oosterschelde estuary (SW Netherlands) during the period 1979–1986. The barrier allows the tides to enter the estuary freely, and, on the other hand, the barrier guarantees safety for the human population and their properties when a stormflood threatens the area.Oosterschelde estuary is isolated from the river input, the rear ends of the ecosystem were separated from the estuary by sea-walls and the strongly decreased tidal exchange with the North Sea induced sheltered circumstances. The Oosterschelde changed from a turbid estuary into a tidal bay, and yet primary production responses appear to be robust and resilient, and the biological communities showed only quantitative shifts from the dominance of specific species assemblages to other assemblages. In many cases predicted changes in the structure of the biological communities could not be verified owing to the large natural variability mainly caused by physical factors (e.g. temperature).     

Influence of Maternal Phenotype on Metabolic Differentiation of Agouti Locus Mutants in the Mouse

The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, A ^vy, or mottled, a^m, mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The A^vy/a and a^m/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.—In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-a^m/a^m mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.—Mottled yellow A^vy/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti A^vy/a siblings.—In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti A^vy/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow A ^vy/a dams produced significantly fewer pseudoagouti A ^vy/a offspring than did black a/a dams.—The data suggest that metabolic differentiation of A^vy/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam.     

The Role of Snowmelt and Spring Rainfall in Inorganic Nutrient Fluxes from a Large Temperate Watershed, the Androscoggin River Basin (Maine and New Hampshire)

The importance of snowmelt and spring rainfall to water and nutrient exports from macro-scale watersheds (>1000 km²) is not well established. Data collected from the Androscoggin River watershed (Maine and New Hampshire) between February 1999 and March 2002 show that the 90-day spring melt period accounted for 39–57% of total annual discharge and is likely driven both by snowpack melting and spring rainfall. While large loads of dissolved inorganic nitrogen (DIN) are delivered to the watershed from snowmelt and rain (from 1.16× 10⁶ to 1.61× 10⁶ kg N over the study years), only one third of this N load is exported from the basin during the snowmelt period (0.40× 10⁶–0.48 × 10⁶ kg N). Despite reduced residence time and temperature limitations on biological N retention, there is a poor mass balance between DIN input to the watershed and the nitrogen exported from mouth of the river. Inferences from a geochemical hydrograph separation suggests that approximately 51–63% of the water leaving the mouth of the Androscoggin river is from these ‘new’ water sources (rain and snowmelt) while 37–49% is from DIN depleted soil and groundwater. Mixing of water from different sources, as well as nutrient retention by dams in the upper watershed, may account for the large discrepancy between DIN inputs and exports from this watershed.     

黄河河龙区间退耕还林前后淤地坝拦沙特征分析

为探究黄河中游河龙区间退耕还林工程实施前后淤地坝拦沙变化特征,采用实地测量和文献集成分析相结合的方法,分析了退耕前后多个时段河龙区间不同分区淤地坝的拦沙特征。结果表明:退耕后,河龙区间北部、中部和南部淤地坝平均拦沙模数分别为7138.5 t km~(-2) a~(-1)、2596.5 t km~(-2) a~(-1)和4230.9 t km~(-2) a~(-1),比退耕前分别减少了49.5%、84.1%和52.1%,且均显著小于退耕前,坝控流域侵蚀程度总体上由极强烈侵蚀、剧烈侵蚀和极强烈侵蚀分别转变为强烈侵蚀、中度侵蚀和中度侵蚀;退耕前河龙区间中部和南部淤地坝拦沙模数随时间推进显著降低;退耕后河龙区间北部淤地坝拦沙模数随时间推进而下降。未来河龙区间淤地坝建设应根据小流域侵蚀产沙现状适当缩减规模,以免造成水土资源浪费,影响下游的用水安全。     

Turbidity,nutrients and phytoplankton primary production in the Oosterschelde (The Netherlands) before,during and after a large-scale coastal engineering project (1980–1990)

Turbidity, nutrient concentrations and phytoplankton primary production were monitored in the Oosterschelde before, during and after the construction of a storm-surge barrier and two compartment dams.Flow velocities and suspended matter concentrations decreased severely, causing an increased transparency of the watercolumn. In the eastern and northern compartments, the previously pronounced seasonal variation disappeared.Reduction of the freshwater load and decreasing nutrient concentrations in the adjacent North Sea coastal waters resulted in lower nitrite + nitrate and silicate concentrations. Autumn phosphate concentrations remained at the same level as before the nutrient reduction. Silicate was a limiting nutrient during the pre-barrier period and nitrogen and silicate were limiting during the post-barrier period.Annual patterns in chlorophyll-a concentrations in the western and central compartments showed no obvious trend; in the eastern and northern compartments higher values were measured from 1985 onwards.Primary production during the period 1980–1990 varied between 176 and 550 g C m^–2 yr^–1. The annual primary production in the western compartment had decreased, while in the central and eastern compartments annual primary production did not change: the formerly existing gradient disappeared. In the northern compartment higher chlorophyll-a concentrations and high annual production suggest that the phytoplankton could benefit from the increased transparency while nutrient concentrations were still high enough to support phytoplankton growth.Changes in photosynthetic physiological parameters were observed which suggested shade adaptation. This is in contrast to improved light conditions and reduced nutrient availability. The apparent incoherence with light-shade adaptation theory may be explained by the species shift that occurred.As a result of the opposite effects of a more favourable light climate and a reduced nutrient availability, together with the resulting species shift, the annual primary production showed a large degree of homeostasis.     

Census of gorillas in northern Republic of Congo

We censused gorilla populations in northern Congo from February to April 1989 and June 1990. The objective was to provide the first quantitative data from a variety of sites on gorilla populations from a country that had unknown but potentially high populations. The method used was a census of nests along strip transects. A total of 401.0 km of transects was sampled in four different study areas. The overall density calculated for all transects was 0.4 nesting gorillas/km². The highest density, 1.2 nesting gorillas/km², was found in the vast Likouala swamp area of north central Congo. The two northern sites showed low densities of 0.1 and 0.2 nesting gorillas/km², respectively. The northwestern site showed an intermediate density of 0.6 nesting gorillas/km². The vegetation type with the highest density was swamp forest with 2.4 nesting gorillas/km². The limited sample presented shows that gorillas are widespread and common in northern Congo, even in the swamp forests previously considered unsuitable as gorilla habitat. It is probable that Congo holds the largest population of gorillas in Africa after Gabon. © 1992 Wiley-Liss, Inc.     

The effect of cascaded huge dams on the downstream movement of <Emphasis Type="Italic">Coreius guichenoti</Emphasis> (Sauvage &amp; Dabry de Thiersant, 1874) in the upper Yangtze River

Huge dams (installed capacity > 100 MKW) are generally built on large rivers that display high biodiversity and include major migration routes for many diadromous and potamodromous fish. As a result, these dams lead to severe ecological impacts and receive more attention than smaller dams. Most previous work on the impact of huge dams on fish downstream movement has focused on a single dam and reservoir, so little is known about the effect of cascaded huge dams and reservoirs on downstream movement. During the period 2012–2014, two huge dams (the Xiangjiaba and the Xiluodu) were constructed on the upper Yangtze River and the reservoir impoundments began, respectively in October 2012 and May 2013. These cascaded hydroelectric projects could have a large adverse effect on the downstream movement of an important potamodromous fish species, Coreius guichenoti. To study the effect of cascaded impact of sequential huge dams and reservoirs on passive and active downstream movement of C. guichenoti, eggs and larvae were collected in the Yibin section during 2012–2014 and fish were collected monthly at a site in the Hejiang section from June 2012 to July 2014. Our results showed that, compared to one huge reservoir and dam, cascaded dams exert a more serious effect and obstruct downstream movement of eggs, larvae and young fish (particularly the yearlings and two-year-olds) of C. guichenoti. Individual C. guichenoti were able to pass with relative ease through one reservoir and dam, but passing through both reservoirs and dams was very difficult. To allow access to the spawning grounds upstream, a fish passage should be built on the Xiluodu dam. However, due to the hydropower development in the whole upper basin, captive breeding and maintaining at least 60 km of riverine habitat upstream of a spawning ground could be a more cost-effective approach to maintaining C. guichenoti populations in the Upper Yangtze River.     

Role of habitat in determining macroinvertebrate production in an intermittent-stream system

1. The effect of channel drying on macroinvertebrate production was studied at the habitat and reach scale in a catchment drained by intermittent streams in Maine, U.S.A. The catchment includes two first‐order streams and their second‐order confluence. Six reaches were selected for study based on differences in channel slope and habitat cover (bedrock, riffle/run, debris dam and pool). Stream water in each reach was acidic and oligotrophic. 2. The study reaches had different degrees of channel drying. In the first‐order reaches, surface flow ceased earlier in the season and for longer periods than second‐order reaches. Regardless of reach, pool and debris dam habitats retained water longer than riffle/runs and bedrock. Unlike other habitats, debris dams retained moisture for relatively long periods following cessation of surface flow. 3. Reach‐specific macroinvertebrate production ranged from approximately 1.7 to 2.9 g AFDM m⁻² year⁻¹ which are among the lowest values ever reported. Habitat‐specific production ranged from approximately 0.5 to 5.0 g AFDM m⁻² year⁻¹ (bedrock and debris dams, respectively). 4. At the reach scale, quantities of stored benthic organic matter (range approximately 200–600 g AFDM⁻²) decreased in a downstream direction. 5. A combination of differences in the timing and duration of channel drying, habitat structure and detritus standing stocks appeared to influence levels of invertebrate production among the study reaches. 6. Our interpretation of a canonical correspondence analysis indicates that drying is more important than habitat in affecting macroinvertebrate production in this intermittent stream system.     

Ecological and economic implications of a tropical jellyfish invader in the Gulf of Mexico

A large population of a previously unreported jellyfish occurred across the northern Gulf of Mexico (USA) from May through September of 2000. The jellyfish, identified as Phyllorhiza punctata by von Lendenfeld (1884), is not indigenous to the Gulf of Mexico or to the Atlantic Basin. Current theory states that this invasive species was introduced into the Atlantic from the Pacific Ocean through the Panama Canal about 45 years ago, and several confirmed reports indicated that a cryptic population may have existed in the northern Gulf since 1993. However, mesoscale hydrographic anomalies in spring 2000 may have directly transported the population from the Caribbean Sea where populations of P. punctata have been reported previously in Puerto Rico. We undertook a rapid-response sampling program from June through September to obtain ecological information regarding P. punctata in the highly productive northern Gulf waters. Jellyfish bell diameter increased by about 50% (from an average of 32 ± 12 to 45 ± 6 cm) as animals invaded nearshore waters during July. As the summer progressed, a net westerly distribution shift followed nearshore currents to an accumulation point near the mouth of Lake Borgne, Louisiana, in the far western Mississippi Sound. In the Lake Borgne aggregation, we estimated 5.37 × 10⁶ medusae over an area of about 150 km². All of the medusae appeared to lack the symbiotic algae that are present in all other described populations, and therefore must have depended solely on planktivory for their nutrition. Clearance rates estimated from ambient zooplankton, gut contents and published digestion times ranged from < 1 m³ d^–1 for adult copepods to over 90 m³ d^–1 for fish eggs. Based on these clearance rates, the central core of this aggregation (30 km²) was being turned over at least once per day with even higher turn-over in very concentrated `super-swarms'. Clogging of shrimp nets was the greatest economic impact, and perhaps contributed to millions of dollars in economic losses. The indirect effect of predation on eggs and larvae of commercially important finfish and shellfish remained intangible in the determination of economic effects. In 2001, P. punctata has recurred along southern Louisiana and has apparently spread into the coastal and lagoonal waters of the Florida east coast.     

Organic matter accumulation in the bottom sediments and its regulatory aspects in the southern basin of Lake Biwa

Approximately 14 million people get their drinking and industrial water from the most southern part of Lake Biwa. This shallow region, however, has been eutrophicated severely from year to year by nutrients loading from both the surrounding inflowing rivers and the north basin. Sedimented solids of the surface layer of bottom sediments are stirred up very frequently by strong winds and waves in this shallow region. Moreover, the water quality has been deteriorated by the release of nutrients from the surface layer of bottom sediments in which organic matter has accumulated. For the period 1989 to 1990, the suspended solids content had a close correlation with the COD value, and the T-N and T-P concentrations in the water of inflowing rivers to the basin. T-N release rate from the surface layer of bottom sediments ranged from 6.3 to 213.8 mg m^-2 d^-1 and the release load was 936 kg d^-1 for the entire 58 km² of the south basin. On the other hand, T-P release rate ranted from 0.91 to 3.56 mg m^-2 d^-1 and the total release load was approximately 69 kg d^-1 in the basin. Suction dredging of organic matter rich sediments was carried out in the basin to improve the water quality. Removed sediments were used after processing for various kinds of construction materials, such as bricks for pavement, walls of domestic houses, and ornamental materials of public buildings.     

黄土高原生态工程对关键生态系统服务时空变化的影响——以延河流域为例

黄土高原地区生态工程的实施,使其生态环境得到显著改善,提高了生态系统服务能力。现有的研究成果中,生态工程对生态系统服务影响的定量评价比较匮乏。以延河流域为例,采用RUSLE模型和InVEST模型对生态系统服务进行评价,通过构建模型识别出不同时期的生态工程区,探究生态工程对生态系统服务的定量影响,为下一步生态工程的实施提供科学的指导和依据。结果表明：(1)2000—2018年,延河流域土壤保持服务和产水服务均呈波动增长趋势,但二者的变化并不同步。(2)4个时期内,能产生生态效应的生态工程区面积呈波动增长趋势,从854 km²增加到1343 km²,在整个流域均有分布,不同时期的重点分布区不同。(3)生态工程增强了区域的土壤保持能力和产水能力,土壤保持服务增强区面积从477.5 km²增加到1140.6 km²,保持的土壤总量从2.1×10⁷ t增加到5.6×10⁷ t;产水服务增强区面积从139.1 km²增加到485.5 km     

Vernal nitrogen and phosphorus retention by forest understory vegetation and soil microbes

Northern hardwood forests experience annual maximal loss of nutrients during spring. The vernal dam hypothesis predicts that spring ephemeral herbs in northern hardwood forests serve as sinks for nutrients during this season and reduce the loss of nutrients from the terrestrial ecosystem. Soil microbes of northern hardwood forests also sequester nutrients during spring. We compared the vernal nutrient acquisition ability of a soil microbial community and an understory plant community with species of mixed leaf phenology. We monitored nitrogen and phosphorus pool sizes in understory vegetation and soil microbes during spring from 1999 through 2001 in a northern hardwood forest in the Catskill Mountains, New York. Vegetation nutrient content increased during two spring seasons by an average of 3.07 g N m^–2 and 0.19 g P m^–2 and decreased during one spring by 0.81 g N m^–2 and 0.10 g P m^–2. Evergreen, wintergreen, and deciduous plant species were able to sequester nutrients during spring. Soil microbial nutrient content decreased during one spring by 1.29 g N m^–2 and remained constant during the other two springs. Streamwater nitrogen losses were not correlated with biotic nutrient uptake suggesting a temporal disconnect between the two processes. We conclude that understory vegetation is a larger potential sink for vernal nutrients than are soil microbes in this northern hardwood forest and understory and species representing multiple phenologies are capable of vernal nutrient uptake.     

Biomass Allocation in Cyperus papyrus in a Tropical Wetland,Lake Naivasha,Kenya1

The nutrient status of Lake Naivasha, a freshwater lake in southeastern Kenya, has been rising since at least 1982. A potential effect of increases in nutrient supply to the lake's floating papyrus is increasing of the plants’ investment in above–water material and reduction of the amount of energy invested in uptake and storage. Biomass and its allocation between culms, panicles, roots, and rhizomes was measured in 17 sites around the 150–km² lake. Although above–water biomass was greatest in sites closest to the lake's major nutrient inflow, the River Malewa, there was little evidence of corresponding decreases in the biomass of uptake and storage tissues. In August 1995, the average ± SD biomass of papyrus in the lake was 11,540 ± 3020 g/m², with the papyrus containing about 4500 ± 1900 g total carbon/m² and about 100 ± 70 g total nitrogen/m². Plant nitrogen contents did not vary with distance from the main external nutrient supply. Together with low nitrogen concentrations in the plants (0.60 ± 0.26 in culms and 0.99 ± 0.50% in rhizomes), very high carbon to nitrogen ratios (49 ± 20:1) and nitrogen fixation in the rhizosphere explaining only about half of the plants’ nitrogen, papyrus is a likely net sink for nitrogen supplied from the lake's increasingly cultivated watershed. Despite this role, clearance of papyrus in favor of agriculture partly explains the reductions in the area of papyrus within the lake basin from 48 km² in the late 1960s to 14 km² in 1995.