Impacts of disturbance on migratory waterfowl

It is well known that disturbance from human activities can cause temporary changes in behaviour and locally affect temporal and spatial distribution of migratory and wintering waterfowl. But it is also known that, to some extent, birds can compensate for disturbance by altering their behaviour or habituating to human activities. Comparatively little is known about how these reactions to disturbance may impact on the large-scale dispersion of waterfowl and, ultimately, on their population dynamics. To be able to answer these questions, a better theoretical framework, based on optimal foraging theory incorporating predation risk, and field experiments are required. Furthermore, we need to study the waterfowl throughout their winter ranges to interpret the overall impacts of disturbance. This paper examines two cases where the impacts of disturbance have been assessed from field experiments. In one study, disturbance effects of shooting were tested by setting up experimental reserves in two Danish coastal wetlands. Over a 5-year period, these became two of the most important staging areas for coastal waterfowl, and the national totals of key species were significantly increased. A national management plan which will establish more than 50 new shooting-free refuges on Danish coastal areas within the next 5 years is likely to boost waterfowl numbers even more. Such retention of birds at more northerly sites on the fiyway should result in a more efficient resource utilization and may positively affect the population dynamics where numbers are affected by winter resources. In a second study, the impacts of disturbance by farmers on spring fattening of Pink-footed Geese Anser brachyrhynchus were analysed. In undisturbed areas in northern Norway, abdominal profiles of the geese increased rapidly, whereas in disturbed sites they did not. Subsequently, geese that had used undisturbed sites reproduced better than geese from disturbed sites.     

Growth responses of Urtica dioica L. to different water table depth

The study has examined the effect of water table depth (WTD) on production, biomass allocation, allometric relationships and transpiration rate in Urtica dioica. The essential importance of WTD for occurence and spread of Urtica has been documented. Water table depths were: 60, 50, 40, 30, 20, and 10 cm below the soil surface. Thirty individuals of Urtica for each WTD, established from apical parts of young rhizomes, has been planted in containers and placed at WTD from the 8th May to the 24th July. The height of all individuals and the length and width of the largest leaf blade of each individual were measured after 42, 55 and 83 days. Transpiration rate was measured after 53 and 82 days. Above-ground biomass of all individuals was harvested on 24 of July and was separated into individual organs. Various biometric parameters were measured. Results showed that biomass, plant height, branching of stems and rhizomes and rhizomes length decreased in containers with a more shallow WTD. Particularly, allometric relationships between plant height and other characteristics such as basal diameter, length of longest branch and rhizome were affected by the water level. The biometric parameters were highly dependent on plant height. Transpiration strongly decreased with decreasing WTD. Therefore, the high water level in the soil suppresses growth of particular organs and water regime of Urtica plants/. Generally, long-term high water content in the soils of floodplains, particularly during floods, limits rapidly, particularly vegetative spread of Urtica in the wetland habitats.     

Carrying capacity of wetlands for massive migratory waterfowl

Although it has been documented that waterfowl can cause water quality problems when their populations are large relative to the size or volume of the water body, the question as to how many waterbirds a wetland or a lake can support remains unanswered. A method to quantify the carrying capacity of a water body with regard to massive waterfowl was developed through the study of five wetlands that are used as the wintering ground by a large number of waterfowl in Japan. It takes into consideration water depth, retention time, and in-lake phosphorus concentration. For one of the sites, Sakata Lagoon, which is a registered Ramsar wetland in Japan, the assessment of its carrying capacity suggests that the number of waterfowl should be reduced by half to sustain the water quality of this wetland. Based on the comparison among the five wetlands, a simple indicator was proposed for quick diagnosis. Moreover, a general plot of permissible loading of phosphorus (kg/ha/year) by waterfowl was presented. Besides, this study shed some new light on potential toxicity and accumulation of waterfowl feces at lakebed. Finally, a proposal to increase the carrying capacity of Sakata Lagoon is discussed.     

Effects of waterfowl on water quality

The effects of Cormorants and 3 species of ducks were studied on the eutrophication of Lake Balaton. The quantity of consumed food and of excrement were estimated. The Cormorants (1500 pairs and their fledglings) inhabiting the area of Kis-Balaton took up 12.5 tonnes of N and 3.1 tonnes of P in 1983. The effects of fish-eating Cormorants can be quantified better than those of ducks which also feed on plant material.     

Ecosystem respiration in a heterogeneous temperate peatland and its sensitivity to peat temperature and water table depth

Background and aims

Ecosystem respiration (R _eco ) is controlled by thermal and hydrologic regimes, but their relative importance in defining the CO₂ emissions in peatlands seems to be site specific. The aim of the paper is to investigate the sensitivity of R _eco to variations in temperature and water table depth (WTD) in a wet, geogenous temperate peatland with a wide variety of vegetation community groups.

Methods

The CO₂ fluxes were measured using chambers. Measurements were made at four microsites with different vegetation communities and peat moisture and temperature conditions every 3 to 4 weeks during the period 2008–2009, 2 years with contrasting WTD patterns. Models were used to examine the relative response of each microsite to variations in peat temperature and WTD and used to estimate annual total R _eco .

Results

Temporal variations in R _eco were strongly related to peat temperature at the 5 cm depth. However, two of the microsites did not show any significant change in this relationship while two others showed contrasting responses including an increase and decrease in temperature sensitivity with deeper WTD. Average R _eco varied among the microsites and tended to be greatest for those with greatest leaf area which also positively correlated with deeper WTD, ash content and degree of peat decomposition at 20 cm. A combined temperature and WTD model explained up to 94 % of the temporal variation in daily average R _eco and was used to show that on an annual basis, R _eco was between 5 and 18 % greater in the warmer year with deeper WTD.

Conclusion

Microsite-specific responses were related to differences in vegetation and peat characteristics among microsites. R _eco may have remained insensitive to WTD variations at one microsite due to the dominance of autotrophic respiration from abundant sedge biomass. At a Sphagnum-dominated microsite, a lack of response may have been due to relatively small variations in WTD that did not greatly influence microbial respiration or due to offsets between decreasing and increasing respiration rates in near-surface and deeper peat. The microsite with the most recalcitrant peat had reduced R _eco sensitivity to temperature under more aerobic conditions while another microsite showed the opposite response, perhaps due to less nutrient availability during the wet year. Ultimately, micro-site specific models with both soil temperature and WTD as explanatory variables described temporal variations in R _eco and highlighted the significant spatial variations in respiration rates that may occur within a single wetland.     

The limiting roles of nitrogen and moisture on Sphagnum angustifolium growth over a depth to water table gradient

Plant and Soil - Lespedeza cuneata is a non-native invasive legume that alters the soil bacterial community, associates promiscuously with rhizobia, and benefits more from rhizobial interactions...     

Effect of water table depth and tillage methods on plant-water status and yield of rice

Summary Effects of water table depths on plant-water status, and on growth and yields of two rice varieties (TOS 78 and TOS 848) were studied in a lysimetric investigation. A field study was also conducted on a hydromorphic soil to investigate the effects of fluctuating water table on rice. The leaf-water potential of TOS 78 monitored at 1300 hours at 50% flowering stage was –17.5 and –23.0 bars for 0 and 60 cm water table depths, respectively. When grown under soil moisture stress, TOS 848 maintained higher leaf-water potential (–17.5 barvs –22.5 bar) and yielded more than TOS 78. Under hydromorphic soil conditions, no-tillage treatments yielded the same as conventionally tilled plots.     

Estimating partial observability and nonlinear climate effects on stochastic community dynamics of migratory waterfowl

1. Understanding the impact of environmental variability on migrating species requires the estimation of sequential abiotic effects in different geographic areas across the life cycle. For instance, waterfowl (ducks, geese and swans) usually breed widely dispersed throughout their breeding range and gather in large numbers in their wintering headquarters, but there is a lack of knowledge on the effects of the sequential environmental conditions experienced by migrating birds on the long-term community dynamics at their wintering sites. 2. Here, we analyse multidecadal time-series data of 10 waterfowl species wintering in the Guadalquivir Marshes (SW Spain), the single most important wintering site for waterfowl breeding in Europe. We use a multivariate state-space approach to estimate the effects of biotic interactions, local environmental forcing during winter and large-scale climate during breeding and migration on wintering multispecies abundance fluctuations, while accounting for partial observability (observation error and missing data) in both population and environmental data. 3. The joint effect of local weather and large-scale climate explained 31·6% of variance at the community level, while the variability explained by interspecific interactions was negligible (<5%). In general, abiotic conditions during winter prevailed over conditions experienced during breeding and migration. Across species, a pervasive and coherent nonlinear signal of environmental variability on population dynamics suggests weaker forcing at extreme values of abiotic variables. 4. Modelling missing observations through data augmentation increased the estimated magnitude of environmental forcing by an average 30·1% and reduced the impact of stochasticity by 39·3% when accounting for observation error. Interestingly however, the impact of environmental forcing on community dynamics was underestimated by an average 15·3% and environmental stochasticity overestimated by 14·1% when ignoring both observation error and data augmentation. 5. These results provide a salient example of sequential multiscale environmental forcing in a major migratory bird community, which suggests a demographic link between the breeding and wintering grounds operating through nonlinear environmental effects. Remarkably, this study highlights that modelling observation error in the environmental covariates of an ecological model can be proportionally more important than modelling this source of variance in the population data.     

On the relationship between water table depth and water vapor and carbon dioxide fluxes in a minerotrophic fen

The focus of this study is the relationship between water table depth (WTD) and water vapor [evapotranspiration (ET)] and carbon dioxide [CO₂; net ecosystem exchange (NEE)] fluxes in a fen in western Canada. We analyzed hydrological and eddy covariance measurements from four snow‐free periods (2003–2006) with contrasting meteorological conditions to establish the link between daily WTD and ET and gross ecosystem CO₂ exchange (GEE) and ecosystem respiration (R_eco; NEE=R_eco?GEE), respectively: 2003 was warm and dry, 2004 was cool and wet, and 2005 and 2006 were both wet. In 2003, the water table (WT) was below the ground surface. In 2004, the WT rose above the ground surface, and in 2005 and 2006, the WT stayed well above the ground surface. There were no significant differences in total ET (～316 mm period^?1), but total NEE was significantly different (2003: 8 g C m^?2 period^?1; 2004: ?139 g C m^?2 period^?1; 2005: ?163 g C m^?2 period^?1; 2006: ?195 g C m^?2 period^?1), mostly due to differences in total GEE (2003: 327 g C m^?2 period^?1; 2004: 513 g C m^?2 period^?1; 2005: 411 g C m^?2 period^?1; 2006: 556 g C m^?2 period^?1). Variation in ET is mostly explained by radiation (67%), and the contribution of WTD is only minor (33%). WTD controls the compensating contributions of different land surface components, resulting in similar total ET regardless of the hydrological conditions. WTD and temperature each contribute about half to the explained variation in GEE up to a threshold ponding depth, below which temperature alone is the key explanatory variable. WTD is only of minor importance for the variation in R_eco, which is mainly controlled by temperature. Our study implies that future peatland modeling efforts explicitly consider topographic and hydrogeological influences on WTD.     

水位埋深和微地貌对金川泥炭土壤微生物活性及甲烷功能基因的影响

泥炭沼泽是长期储存碳最有效的陆地生态系统.水文特征和微地貌可能会通过调控微生物群落和功能影响泥炭地碳储存.本研究以长白山金川泥炭沼泽为研究对象,选取-10、-1、0、4、10、13、14和18 cm八个水位埋深,并在各水位埋深点采集臌囊薹草(Carexs chmidtii)草丘和丘间微地貌的土壤样品,以探究水位埋深和微...     

Isolation of type a influenza viruses from the migratory waterfowl along the Mississippi flyway.

Four type A infleunza viruses were isolated from tracheal swabs taken from apparently healthy ducks (mallards, Anas platyrhynchos) along the Mississippi flyway in Minnesota. Inital identification of group A influenza was made possible by the use of the agar gel precipitin test.     

水层厚度变化对稻田能量分配的影响

稻田土表因存在水层厚度变化和干湿交替,导致垂直方向的能量收支状况发生改变。本文采用逐时多元回归方法,分析了水层、叶面积及气象因子对各能量贡献,并选取典型相似天气以规避能量输入差异、按叶面积划分以规避植冠层结构差异,定量研究了稻田水层厚度变化对稻田能量分配的影响。结果表明:白天,随稻田水层厚度增加,水层储热量也增大,导致水面热通量增大,从而降低了稻田潜热通量,这种作用在水稻冠层稀疏时期尤其明显;在冠层密集时,到达水面的净辐射能量被削弱,水层厚度对潜热通量的调节作用降低;由于稻田感热通量总体较低,水层厚度的变化对其影响小,调节作用不明显;双源蒸散模型模拟揭示,水面潜热随水层深度增加而减少是导致总潜热降低的主要原因,且在水稻冠层稀疏时期表现明显。     

Interactions among fungal community structure, litter decomposition and depth of water table in a cutover peatland

Peatlands are important reservoirs of carbon (C) but our understanding of C cycling on cutover peatlands is limited. We investigated the decomposition over 18 months of five types of plant litter (Calluna vulgaris, Eriophorum angustifolium, Eriophorum vaginatum, Picea sitchensis and Sphagnum auriculatum) at a cutover peatland in Scotland, at three water tables. We measured changes in C, nitrogen (N) and phosphorus (P) in the litter and used denaturing gradient gel electrophoresis to investigate changes in fungal community composition. The C content of S. auriculatum litter did not change throughout the incubation period whereas vascular plant litters lost 30-40% of their initial C. There were no differences in C losses between low and medium water tables, but losses were always significantly less at the high water table. Most litters accumulated N and E. angustifolium accumulated significant quantities of P. C, N and P were significant explanatory variables in determining changes in fungal community composition but explained <25% of the variation. Litter type was always a stronger factor than water table in determining either fungal community composition or turnover of C, N and P in litter. The results have implications for the ways restoration programmes and global climate change may impact upon nutrient cycling in cutover peatlands.     

Nutrient additions by waterfowl to lakes and reservoirs: predicting their effects on productivity and water quality

Lakes and reservoirs provide water for human needs and habitat for aquatic birds. Managers of such waters may ask whether nutrients added by waterfowl degrade water quality. For lakes and reservoirs where primary productivity is limited by phosphorus (P), we developed a procedure that integrates annual P loads from waterfowl and other external sources, applies a nutrient load-response model, and determines whether waterfowl that used the lake or reservoir degraded water quality. Annual P loading by waterfowl can be derived from a figure in this report, using the days per year that each kind spent on any lake or reservoir. In our example, over 6500 Canada geese (Branta canadensis) and 4200 ducks (mostly mallards, Anas platyrhynchos) added 4462 kg of carbon (C), 280 kg of nitrogen (N), and 88 kg of P y^–1 to Wintergreen Lake in southwestern Michigan, mostly during their migration. These amounts were 69% of all C, 27% of all N, and 70% of all P that entered the lake from external sources. Loads from all external sources totaled 840 mg P m^–2 y^–1. Application of a nutrient load-response model to this concentration, the hydraulic load (0.25 m y^–1), and the water residence time (9.7 y) of Wintergreen Lake yielded an average annual concentration of total P in the lake of 818 mg m^–3 that classified the lake as hypertrophic. This trophic classification agreed with independent measures of primary productivity, chlorophyll-a, total P, total N, and Secchi disk transparency made in Wintergreen Lake. Our procedure showed that waterfowl caused low water quality in Wintergreen Lake.Contribution 824 of the National Fisheries Research Center-Great Lakes, 1451 Green Road, Ann Arbor, Michigan 48105, U.S.A. and 722 of the Kellogg Biological Station, Michigan State University.