Genetic differentiation of Elysia timida (Risso, 1818) populations in the Southwest Mediterranean and Mar Menor coastal lagoon

Genetic variation at 10 enzyme loci was analysed in Elysia timida sacoglossan mollusc samples, originating from both coastal lagoon and marine sites. The observed heterozygosity ranged from 0.390 (Los Urrutias) to 0.277 (Tabarca). Marine and coastal lagoon populations were characterised by exclusive alleles.     

Dynamics and management of some coastal dune woodlands near The Hague,The Netherlands

Changes are reported of Crataegus-Betula dune woodlands between 1950–1980 from Meijendel, a calcareous coastal dune system near the city of The Hague, The Netherlands, which is used as a water catchment area. It concerns both woodlands in degradation stage and, more common, woodlands on the increase. Changes were recorded with help of successive vegetation maps, air photos and permanent plot observations. Woodland increase usually occurs on places with groundwater at or near the surface, either because of natural circumstances or as a result of artificial groundwater recharge through infiltration as part of the water catchment activities. The management of both types of woodland is discussed.Nomenclature follows Heukels-van der Meijden (1983), Flora van Nederland, 20th ed. Wolters-Noordhoff, Groningen. Nomenclature of mosses follows Margadant & During (1982), Beknopte Flora van Nederlandse Blad- en Levermossen, Thieme, Zutphen.The authors have pleasure in thanking their colleagues from the Dune Water Works who supplied data on hydrology.     

Stable isotope-based statistical tools as ecological indicator of pollution sources in Mediterranean transitional water ecosystems

N-stable isotope analysis of macroalgae has become a popular method for the monitoring of nitrogen pollution in aquatic ecosystems. Basing on changes in their δ¹⁵N, macroalgae have been successfully used as biological traps to intercept nitrogen inputs. As different nitrogen sources differ in their isotopic signature, this technique provides useful information on the origin of pollutants and their extension in the water body. However, isotopic fractionation potentially resulting from microbial nitrogen processing, and indirect isotopic variations due to effects of physicochemical conditions on algal nutrient uptake and metabolism, may affect anthropogenic N isotopic values during transportation and assimilation. This in turn can affect the observed isotopic signature in the algal tissue, inducing isotopic variations not related to the origin of assimilated nitrogen, representing a “background noise” in isotope-based water pollution studies.In this study, we focused on three neighbouring coastal lakes (Caprolace, Fogliano and Sabaudia lakes) located south of Rome (Italy). Lakes were characterized by differences in terms of anthropogenic pressure (i.e. urbanization, cultivated crops, livestock grazing) and potential “background noise” levels (i.e. nutrient concentration, pH, microbial concentration). Our aim was to assess nitrogen isotopic variations in fragments of Ulva lactuca specimens after 48 h of submersion to identify and locate the origins of nitrogen pollutants affecting each lake. δ¹⁵N were obtained for replicated specimens of U. lactuca spatially distributed to cover the entire surface of each lake, previously collected from a benchmark, unpolluted site. In order to reduce the environmental background noise on isotopic observations, a Bayesian hierarchical model relating isotopic variation to environmental covariates and random spatial effects was used to describe and understand the distribution of isotopic signals in each lake.Our procedure (i) allowed to remove background noise and confounding effects from the observed isotopic signals; (ii) allowed to detect “hidden” pollution sources that would not be detected when not accounting for the confounding effect of environmental background noise; (iii) produced maps of the three lakes providing a clear representation of the isotopic signal variation even where background noise was high. Maps were useful to locate nitrogen pollution sources, identify the origin of the dissolved nitrogen and quantify the extent of pollutants, showing localized organic pollution impacting Sabaudia and Fogliano, but not Caprolace. This method provided a clear characterization of both intra- and inter-lake anthropogenic pressure gradients, representing a powerful approach to the ecological indication and nitrogen pollution management in complex systems, as transitional waterbodies are.     

Recovery of15N-labelled fertilizer by Coastal bermudagrass in lignite minesoil

Minesoils developed from lignite surface mining in Texas are nutrient-poor and have a high N retention capacity. A major concern of landowners and soil conservationists is the response of Coastal bermudagrass to the application of low rates of ammonium-N fertilizer on these nutrient-poor minesoils. A glasshouse study, using¹⁵N-labelled ammonium sulfate fertilizer and lignite minesoil, was conducted to measure Coastal bermudagrass biomass production and fertilizer recovery during establishment in response to clipping at 2, 4, and 8 week intervals. At N rates of 0, 40, and 80 kg N ha^–1,increases in N fertilization increased Coastal bermudagrass aboveground biomass 5-fold, but showed only small increases in belowground biomass. Recovery of ammonium-N fertilizer ranged from 54 to 63%. Roots contained approximately the same N content across all fertilizer rates suggesting that young, estabilishing, Coatal bermudagrass roots reserve N until their N requirement is met. As more N is obtained above that which was needed to maintain roots, then additional N taken up by the plant was transported to aboveground plant parts for growth. Frequent clipping intensified N transport to aboveground tissues. Reduced amounts of N were contained in roots after clipping due to reductions in root growth, biomass, and resource demand. Fertilization of Coastal bermudagrass at low N rates with different N fertilizer forms influenced the distribution of N in the plant and affected N recovery by different parts of the plant.     

Tasmania revisited: rotifer communities and habitat heterogeneity

The results of four field surveys for Rotifera in Tasmania are summarized. Most new species and records in a 1987 survey were from acid waters (pH < 4.0) of dune lakes on the west coast (42° S). Marked intra- and interhabitat differences in rotifer communities of lakes and ponds were demonstrated by cluster analysis and related to habitat heterogeneity.     

Limnology of naturally acidic,oligotrophic dune lakes in subtropical Australia,including chlorophyll — phosphorus relationships

This study provides the most comprehensive physico-chemical and phytoplankton data yet available for Australian dune lakes, which are among the world's most naturally acidic and oligotrophic freshwaters. Seasonal and spatial variations were examined in Blue Lagoon and Lake Freshwater, two ‘water-table window’ lakes in south-east Queensland. Like other dune lakes, they are acidic (minimum pH 4.20 and 4.55, respectively), polymictic water bodies with low concentrations of marine-derived major ions and almost undetectable levels of trace metals. While linmologically similar in winter, during spring-summer Lake Freshwater has significantly higher levels of chlorophyll-a, total phosphorus (TP) and turbidity than Blue Lagoon and other dune lakes, indicating seasonal mesotrophy. The key nutrient is TP, which has recently increased to a maximum of 17 μ· l⁻¹, due either to inputs from recreational sources, or to the death and decomposition of littoral vegetation resulting from falling water levels over the last decade. Inorganic nitrogen, though present only in small amounts, does not appear to limit the eutrophication process because of a shift in phytoplankton dominance from the usual desmids and dinoflagellates to N₂-fixing blue-green algae. A chlorophyll - TP linear regression derived for dune lakes indicates that at TP < 20 μg · l⁻¹ chlorophyll ‘yield’ is higher than in other lake types represented by regressions from the literature. This may be due to a more efficient utilization of the limited available phosphorus by dune lake algae which have adapted to the naturally oligotrophic environment. The implications of these findings for lake management are discussed.     

New ecological information onScytalina cerdale (Pisces: Scytalinidae) from a central California rocky intertidal zone

Synopsis New information regarding the ecology ofScytalina cerdale was obtained over a four year period as a consequence of a long-term marine ecological study at the Diablo Canyon Power Plant (DCPP), San Luis Obispo County, California. Twenty intertidal fish surveys were conducted at approximately quarterly intervals, between March 1979 and June 1983, at three separate rocky shore locations (stations). During each survey, a total of 108 square meters (36 m² per station) was searched for fish during periods of low tide. A total of 280S. cerdale were collected, identified, measured, and released back into the same 4 m² area, from the same intertidal station (Diablo Cove), throughout the study period. This limited intertidal occurrence most likely reflectsS. cerdale microhabitat requirements; a combination of intertidal elevation (mean = +0.3 MLLW), substratum specificity (loose gravel, 5–10mm size range, overlying a base of sand and shell fragments), and degree of wave exposure (semi-protected). Throughout the study,S. cerdale was seasonally more abundant during summer months (June through August) and less abundant during winter months (November through February). The only exception to this abundance trend followed the 1982 winter storms, which coincided with an El Niño event, whenS. cerdale abundance uncharacteristically dropped during the subsequent 1983 spring and summer surveys. Mean total lengths did not vary greatly, reflecting the absence of early juvenile fishes, and relatively high mean fish densities (3.5 fish per m² for 20 surveys) were recorded. Qualitative comparisons betweenS. cerdale abundance and seasonal changes in water temperature indicated an inverse relationship. Gravid females, demersal egg masses, and early juvenile individuals were never observed during the four years of the study. This suggests that unlike most other intertidal fishes, particularly other blennioids,S. cerdale may not utilize the intertidal zone for reproductive and recruitment purposes; Diablo Canyon is the most southerly reported distribution for this intertidal species, and therefore, may not entirely represent the species' biology as a whole.     

人工樟子松—差不嗄蒿植被及其固沙作用

植物固沙是整治沙漠和沙漠化土地的一种有效措施。人工植被的建立是植物固沙的必然结果。人工植被的演替、稳定性及其对环境的影响直接关系到流沙的固定程度。因此,本文旨在探讨人工樟子松(Pinus sylvestris var.     

沿海防护林防海煞危害初探

通过后牧村海岸防护林带附近空气中主要盐离子飘尘的观测分析表明,林带对大气盐尘的吸附和截留作用,无林带地区平均沉降量为４．３μｇ．ｍ＾－３．１００ｍ＾－１,通过林带时为１８．４μｍ＾－３．１００ｍ＾－１。林带的吸队量与树种、枝叶形状有关,侧柏对Ｃｌ＾－和Ｎａ＾＋的吸附量分别为６３３０和３３５０ｍｇ．ｋｇ＾－１,而黑松为１５７０和９５０ｍｇ．ｋｇ＾－１,空气中盐尘受天气条件特别是风速的影响,阴天,风速