Analyses of landuse change impacts on catchment runoff using different time indicators based on SWAT model

Previous researches mainly focused on the runoff responses to landuse change based on annual, seasonal or monthly time scales, there are few studies based on daily scale. We conducted a comprehensive investigation into runoff responses on the daily scale as well as annual and monthly time scales using SWAT, and compared the impacts of time scales with different time indicators quantitatively. Jinjiang, a coastal catchment of southeast China with a humid sub-tropical climate, was used for simulations. A calibrated SWAT model produced satisfactory reproduction of annual, monthly and daily runoff processes over a nine-year (2002–2010) period at three gauging stations. Runoff was then simulated and compared using the same meteorological input but two different landuse scenarios (1985 and 2006, with reduced forest and increased cropland and urbanized area). The results showed varying change in runoff among three time scales and three catchments. The annual runoff had the smallest increase between two scenarios, monthly runoffs had medium rates (increasing in all months except October–November), and daily runoff had the largest rates with the increase in flood peaks but decrease in drought flows, because of the variable influence on interception/evapotranspiration loss, percolation and antecedent soil water storage. Indicators of different time scales (annual runoff, monthly runoff, maximum 1-day and 5-day flood runoff, minimum 1-day and 7-day runoff) proved appropriate for analysing landuse change impacts.     

The impact of site conditions and seed dispersal on restoration success in alluvial meadows

Abstract. We studied the restoration success of flood plain meadows in the northern Upper Rhine valley, where between 1988 and 1992, 35 ha of arable land was converted into grassland and subsequently managed for nature conservation. Remnant populations of typical alluvial meadow species were found in old meadows and along drainage ditches that dissect the whole area. We analysed the site conditions and phytosociological relevés in old and new meadows. Small differences in site parameters between old and new meadows contrasted with a clear floristic differentiation between the two meadow types. The vegetation of old meadows was much more differentiated along prevailing environmental gradients than the vegetation of new meadows. Despite the favourable site conditions for the re‐establishment of species‐rich meadows on the former arable land, restoration success was limited to the vicinity of remnant stands. In contrast to old meadows, indicator species of new grassland were still typical species of regularly disturbed ruderal and arable habitats, often capable of building up a persistent seed bank. The precise mapping of 23 target species revealed that even wind dispersal predominantly leads to re‐establishment in the close circumference of parent plants. We found no indication that regular flooding, hay‐making and autumnal grazing had an impact on recolonization of newly created grassland. Even under favourable conditions for the re‐establishment of target species, restoration success in alluvial meadows proved to be strongly dispersal limited. We discuss the implications of our findings for future restoration management in grasslands.     

Variation of cytosine methylation in response to water availability in two contrasting growth types of an amphibious plant Alternanthera philoxeroides

We used methylation-sensitive amplified polymorphisms (MSAP) to examine the alterations of cytosine methylation in two contrasting growth types of an amphibious plant Alternanthera philoxeroides in response to change of water availability. Using 34 pairs of selective primer combinations, we amplified 1026 and 1128 clear and reproducible bands in root and leaf of A. philoxeroides, respectively. When the aquatic types of plants were transplanted into drought culture, we found a decrease in the overall DNA methylation. When the terrestrial types of plants were transferred into flood culture, we detected a higher frequency of methylation than demethylation events. Alterations of DNA methylation were more evident in root than in leaf in response to change of water availability. When the confounding effects of variable environmental factors were removed, differences of cytosine methylation profiles were observed between two growth types of plants under common growth conditions.     

Short-term succession dynamics of macrobenthos in a salinity-stressed estuary

It is postulated that early succession is influenced by environmental conditions directly after a disturbance event and the temporal scale of succeeding disturbances. For example, Rincon Bayou, Texas, U.S.A. is an estuary stressed by large fluctuations in salinity ranging from oligohaline to hypersaline conditions; leading to the question: are benthic succession dynamics interrupted or affected by the temporal scale of salinity fluctuations? To answer this question, succession dynamics were investigated by manipulation of 1) initial environmental conditions, and 2) time between severe disturbances. The influence of environmental conditions and time course of succession were investigated by comparing two experiments. A synoptic-deployment experiment where samples were deployed at the same environmental conditions and a synoptic-retrieval experiment where samples were collected from deployments under different environmental conditions. Both experiments were conducted at varying time courses of 2-, 4- and 8-week durations between severe disturbances. Severe disturbances were simulated with defaunated sediment. Ambient conditions were simultaneously sampled as a reference. Environmental conditions directly affected succession. In the ambient study, succession occurred in conjunction with changes in environmental conditions. In the synoptic-deployment and synoptic-retrieval studies, environmental conditions at the time of retrieval were more important in determining community structure than deployment duration or initial environmental conditions at time of deployment. Initial environmental conditions were not the primary mechanism in regulation of succession because succession is likely interrupted by frequent salinity disturbances. The salinity-stressed estuary of Rincon Bayou appears to be in a constant state of early and intermediate succession because of frequent salinity-related disturbances.     

Reconstruction of human influence during the last two centuries on two small oxbow lakes near Warsaw (Poland)

Short sediment cores from two small oxbow lakes located in the Vistula valley near Warsaw (Poland) were analysed for chemical composition and zooplankton (Cladocera) remains. The results of these analyses were evaluated using ordination techniques and the results were used to reconstruct the history of human impact of the lakes. The cores were dated using the ²¹⁰Pb method. These analyses show that the collected sediments (60 cm- and 67 cm-long-cores) were deposited during the last 150–200 years. Cladocera assemblages were different in the two lakes; however, Bosmina longirostris was dominant among subfossil Cladocera species in both lakes. The presence of this species indicates the high trophic state of the lakes. Changes in Cladocera species composition suggest that a significant increase in the lakes’ trophic levels has occurred since the 1920s. The change could be related to the construction of flood dikes along the river Vistula, the isolation of the studied lakes from the river, changes in land use, or some combination of these factors. The chemical composition of sediments, particularly the increase in phosphorus and sulphur concentrations, confirms that the construction of dikes against flood was the major factor inducing eutrophication of the oxbow lakes. This study shows that the Warsaw small water bodies are especially sensitive to local disturbances caused by human activity, mainly water management, land use changes and agriculture. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Estimating biogeochemical and biotic interactions between a stream channel and a created riparian wetland: A medium-scale physical model

Straightened channels and altered and drained adjacent riparian wetlands have adversely impacted streams and rivers throughout the US Midwest. This research investigated the biological connection and water quality of a 0.07 ha diversion wetland and adjacent stream at the Olentangy River Wetland Research Park in central Ohio. Before the flowthrough conditions were established, we demonstrated with mark and recapture techniques that the wetland already was a biorefuge for fish under extreme conditions; two species (Centrarchidae) captured in the stream before a total drawdown of the stream were found in the wetland a year later. In addition, water at the bottom remained at around 4 °C over the winter likely due to groundwater input, which possibly provided a warmer shelter for fish. Stream water quality of the lower section, downstream of the wetland outlet, generally improved with hydrologic pulsing in spring after flow-through reconnection due to the trapping of nutrients in the wetland. Mean removal per flood pulse for nitrate-nitrite, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP) were 1.81 g-N m⁻² per pulse, 1.02 g-N m⁻² per pulse, 0.014 g-P m⁻² per pulse, and 0.004 g-P m⁻² per pulse, respectively. The wetland exported 2.8 g-C m⁻² per pulse of organic carbon. A greater attenuation of NO₃⁻ and TP occurred in the marshy outlet channel section of the wetland than the open water section. The diversion wetland successfully removed nitrate and phosphorus during storm pulses in spring. Similar designs should be applied to other locations to examine their function under different climatic and hydrological conditions.     

河流沿线土地利用对策的研究

河流沿线土地是与河流、湖泊的生态学过程紧密相连,直接受洪水影响的沿河（湖）土地带,本文以生态学原理为指导,结合中国森林生态网络工程体系建设理论,对河流沿线土地安全和土地利用的原则、指导思想、理论依据及对策等问题进行了探讨,河流沿线土地安全包括土地的生态效闪安全、经济效益安全与社会效益安全3个方面,土地利用策略的原则是要确保三者的统一,找到三者的最佳结合部,土地利用的指导思想是要把治理与开发紧密结合起来,通过各种措施加强土地的安全建设,实行以增加林木比重为主的近自然的利用和管理对策,根据河流特征的地域分异来确定不同河流,不同河段的利用模式,并基于洪水干扰的风险等级和河流沿线土地的空间分异规律,诊为在河流沿线的纵向上,分别中下游不同河实施人为干扰程度不同的管理对策;横向上按照土地分异性和洪水安全性,分别弹性利用带、脆弱利用带和稳定利用带3条不同土地带采取不同的利用对策。     

The effects of nutrient pulsing on the threatened,floodplain species,Boltonia decurrens

Prior to anthropogenic disturbance, the floodplains of the Illinois River (USA) experienced moderate, cyclical flooding; a phenomenon termed a 'flood pulse'. Significant changes in the hydrology of the Illinois River caused by human alteration of the river channel resulted in a decline in populations of Boltonia decurrens, a native, herbaceous floodplain species of the Illinois River Valley and the demography of the species and underlying mechanisms causing the severe decline of B. decurrens are currently being studied. One component of the river flood pulse is the increased availability of nutrients in floodplain soils. We studied the effects of increased nutrient availability on growth and reproduction of B. decurrens and Aster pilosus, a species replacing B. decurrens in the floodplain. In this study, we examined the effects of a spring nutrient pulse and a late summer nutrient pulse, as compared to a control treatment, on rosettes of B. decurrens and A. pilosus grown in three soil types: sandy loam, silty loam and clay. Biomass, plant height, inflorescences per plant, seed production, and seed mass were measured and compared. Individuals of B. decurrens grown in sandy loam, the predominant soil type of the Illinois River Valley, had thegreatest increase in growth and fecundity in response to nutrient pulsing. Total biomass and inflorescences per plant were significantly greater than the control regardless of the timing of the nutrient pulse. Aster pilosus did not exhibit a clear pattern of increased growth and fecundity in a specific soil type or pulse treatment. The early pulse treatment appeared to have a greater effect across the range of soil types than the late pulse treatment; however, it did not seem to influence any particular variable(s) that we measured. A pulse of nutrients benefits B. decurrens more than A. pilosus, particularly in sandy loam. The increased vigor and fecundity of B. decurrens with a nutrient pulse could be a factor contributing to population survival during the period between disturbance events.