Evidence for Ph Insensitivity in Some Insects Inhabiting Peat Pools in the Loch Fleet Catchment

The impact of liming on the insects associated with peat pools was studied in the Loch Fleet catchment in 1991 and 1992. Fifty-six taxa were identified from 121 timed samples. Despite the raised pH associated with liming in 1986, the population densities of Odonata, Hemiptera and Coleoptera appeared to be unaffected when compared with those of untreated peat pools in the same area. the study demonstrated the existence of two main types of community, that of the steep-sided edges of pools, dominated by odonate nymphs and large species of beetles, and that of the shallower pools, dominated by Hydroporus species (Col., Dytiscidae).     

Role of peat organic matter on isotopic composition of most abundant benthic organisms in intertidal habitats of SW Iceland

The transfer of peat organic matter (OM) from tidal pools of upper littoral to downstream rocky shores and its potential incorporation into marine biota were investigated using the stable isotope approach. Samplings were carried out in September 2004 in two SW Icelandic sites (Osar and Hvassahraun), where we selected (1) areas with shores where grass gently declined towards rocks and, on reaching the sea line, formed small tidal peat pools and (2) areas where grass and rocky shores were not contiguous, rather the grass lower limits were several hundreds of meters back from the shore. In both grass and no grass areas, in the intertidal zone, all benthic organisms and all potential OM sources were sampled. Dominant macroalgae were Ascophyllum nodosum ([Linnaeus] Le Jolis) and Fucus vesiculosus Linnaeus. In grass sites, organisms partially reflected the isotopic composition of peat OM, while in no grass sites, peat represented only a negligible amount of available OM, or its signal was totally absent from the environment. Intertidal organisms could rely on peat both directly by suspension feeding, grazing or scavenging and indirectly by predation (crabs) on low level consumers (barnacles).     

石灰泥炭对镉铅锌污染土壤上小白菜生长和元素吸收的影响

采用盆栽方法研究了在镉、铅、锌污染土壤上,石灰和泥炭对小白菜生长状况及对污染元素(Ｃｄ,Ｐｂ,Ｚｎ)和养分元素(Ｎ,Ｐ,Ｋ,Ｃｕ,Ｍｎ,Ｆｅ)吸收的影响。结果表明,石灰消除了重金属的毒害症状．显著促进小白菜的生长、显著抑制小白菜对镉、铅、锌的吸收。石灰对氮、钾、铜、锰的吸收也有显著抑制作用。泥炭对小白菜生长的改善效果及对铜、铅、锌吸收的抑制效果较石灰差。提高酸性土壤ｐＨ值是减少作物对重金属吸收的有效方法。     

Food and habitat choice in floating seaweed clumps: the obligate opportunistic nature of the associated macrofauna

The species composition of macrofauna associated with floating seaweed rafts is highly variable and influenced by many factors like spatial and temporal variation, period since detachment and probably also the seaweed species. The presence of seaweed preferences was assessed by a combination of in situ seaweed samplings and multiple-choice aquarium experiments in a controlled environment, using the seaweed-associated grazing organisms Idotea baltica and Gammarus crinicornis. Results from the sampling data confirm that the seaweed composition influences macrofaunal species composition and abundance: samples dominated by Sargassum muticum displayed higher densities but lower diversities compared to samples dominated by Ascophyllum nodosum and Fucus vesiculosus. Seaweed preference was also apparent from the multiple-choice experiments, but did not exactly match the results of the community analysis: (1) I. baltica had high densities in seaweed samples (SWS) dominated by F. vesiculosus and A. nodosum, while in the experiments, this isopod was most frequently associated with Enteromorpha sp. and F. vesiculosus, and fed mostly on S. muticum, A. nodosum and Enteromorpha sp.; (2) G. crinicornis had high densities in SWS dominated by F. vesiculosus, while in the experiments, this amphipod was most frequently associated with S. muticum, but fed most on A. nodosum and F. vesiculosus. It is clear from the laboratory experiments that preference for habitat (shelter) and food can differ among seaweed species. However, food and habitat preferences are hard to assess because grazer preference may change if choices are increased or decreased, if different sizes of grazers are used, or if predators or other grazers are added to the experiments. The effects of seaweed composition may also be blurred due to the obligate opportunistic nature of a lot of the associated macrofaunal species.     

Responses of Some Terrestrial Invertebrates to Catchment Treatments Applied at Loch Fleet

The impact of liming and heather-burning on the beetle and spider faunas of open and afforested moorland was studied by use of pitfall traps. of the 168 species identified, the catch of only one species, the ground beetle Trechus obtusus Erichson, increased in a way that could be related to intervention treatments. No species obviously declined as a result of the intervention treatments.     

Recovery of corals a decade after a bleaching event in Dubai, United Arab Emirates

Elevated sea surface temperatures in the late 1990s were associated with widespread coral mortality in the Arabian Gulf, particularly in Acropora dominated areas. This study investigates the composition, condition, and recruitment patterns of coral communities in Saih Al-Shaib, Dubai, United Arab Emirates, a decade after mass bleaching. Five statistically distinct communities were identified by cluster analysis, with grouping optimized from 17 significant indicator species. Overall, 25 species of scleractinian coral were observed, representing 35 ± 1.6% coral cover. Densities of recruits were low (0.8 ± 0.2 m⁻²), and composition generally reflected that of the surrounding adult community. Ten years after mass mortality, Acropora dominated assemblages were observed in three of the six sites examined and coral cover (41.9 ± 2.5%) was double post-bleaching cover. One shallow near-shore site appears to have had recovery of Acropora reset by a further bleaching event in 2002. However, the prevalence of young Acropora colonies here indicates that recovery may recur in several years. One area formerly dominated by Acropora is now dominated by faviids and poritids, with adult and juvenile composition suggesting this dominance shift is likely to persist. Porites lutea and Porites harrisoni dominated communities were negligibly impacted by the bleaching events, and the limited change in coral cover and composition in intervening years likely results from slow growth and low recruitment. Despite strong recovery of several dominant Acropora species, five formerly common species from this area were not observed suggesting local extinction. Dubai coral communities exhibit both resistance and resilience to elevated sea temperatures. The conservation of these patch reefs is warranted given the predicted increase in bleaching events, and the role that these communities may play in regional recovery.     

Monitoring spatio-temporal variation in molluscan grazing pressure in seasonal, tropical rock pools

In Hong Kong, low-shore rock pools support a patchy mosaic of different successional stages of crustose coralline algae. Echinoid and molluscan grazers are abundant in these low-shore rock pools and spatial and temporal variation in grazing pressure is thought to play an important role in structuring these assemblages. Direct records of graze marks using a modified wax-disc method were used to monitor spatial (different pools) and temporal (periods, 3 or 4 days each; spring vs. neap tides; summer vs. winter) variations in grazing pressure. Radula marks of Chlorostoma argyrostoma, Lunella coronata and Nerita albicilla were common in all pools. Grazing pressure was highly variable with tidal state and season but also within these two factors. Lunella and Nerita exerted highest grazing pressure at neap tides during summer, whilst Chlorostoma exerted highest grazing pressure in winter. Although overall patterns of temporal variation were similar and consistent in all pools, there was between pool variation in grazing pressure and individual species showed different patterns. Within the seasonal and tidal variations, large period-to-period differences were found for all species, illustrating small-scale temporal variation. Fine-scale spatial and temporal patterns of variation in grazing pressure of different species, therefore, contribute to the highly dynamic nature of these low-shore rock pools.     

Long-term dynamics of biotic and abiotic resistance to exotic species invasion in restored vernal pool plant communities

Invasion of native ecosystems by exotic species can seriously threaten native biodiversity, alter ecosystem function, and inhibit conservation. Moreover, restoration of native plant communities is often impeded by competition from exotic species. Exotic species invasion may be limited by unfavorable abiotic conditions and by competition with native species, but the relative importance of biotic and abiotic factors remains controversial and may vary during the invasion process. We used a long-term experiment involving restored vernal pool plant communities to characterize the temporal dynamics of exotic species invasion, and to evaluate the relative support for biotic and abiotic factors affecting invasion resistance. Experimental pools (n=256) were divided among controls and several seeding treatments. In most treatments, native vernal pool species were initially more abundant than exotic species, and pools that initially received more native seeds exhibited lower frequencies of exotic species over time. However, even densely seeded pools were eventually dominated by exotic species, following extreme climatic events that reduced both native and exotic plant densities across the study site. By the sixth year of the experiment, most pools supported more exotics than native vernal pool species, regardless of seeding treatment or pool depth. Although deeper pools were less invaded by exotic species, two exotics (Hordeum marinum and Lolium multiflorum) were able to colonize deeper pools as soon as the cover of native species was reduced by climatic extremes. Based on an information-theoretic analysis, the best model of invasion resistance included a nonlinear effect of seeding treatment and both linear and nonlinear effects of pool depth. Pool depth received more support as a predictor of invasion resistance, but seeding intensity was also strongly supported in multivariate models of invasion, and was the best predictor of resistance to invasion by H. marinum and L. multilorum. We conclude that extreme climatic events can facilitate exotic species invasions by both reducing abiotic constraints and weakening biotic resistance to invasion.     

Meiofauna on the seagrass Thalassia testudinum: population characteristics of harpacticoid copepods and associations with algal epiphytes

The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex König meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology.     

Food resource use in a tropical eastern Pacific tidepool fish assemblage

An understanding of the trophic organization patterns of tropical littoral fish assemblages can contribute to the knowledge of key ecosystem processes while simultaneously assisting to validate large-scale biogeographic patterns (i.e. latitudinal patterns in fish herbivory). In the present study, the diets of eight fish species inhabiting the tide pools of a rocky shore on the western coast of Colombia (tropical eastern Pacific) are documented. A total of 17 prey items were identified, with a major representation (average percent by weight) of crabs and macroalgae items in the guts of all species. Small crustacean prey items (crabs, shrimps, copepods and amphipods) dominated the diets of most species, but consumption of macroalgae and diatoms by a significant number of species was also observed. We identified four significant trophic guilds within the assemblage using multivariate techniques (cluster analysis and nMDS): an omnivorous guild, consisting of Malacoctenus zonifer and the smallest size class of Bathygobius ramosus; a small-prey carnivorous guild, consisting of the intermediate size classes of B. ramosus and the smallest size class of Gobiesox adustus; a large-prey carnivorous guild, consisting of both largest size classes of B. ramosus and G. adustus; and an herbivorous guild consisting of Abudefduf concolor, A. troschelii and Chaenomugil proboscideus. The diet of two species slightly overlapped those of the rest of the assemblage and did not conform to any guild (Echidna nocturna and Halichoeres aestuaricola). It is hypothesised that guild formation may be a consequence of aggregation of species at abundant resources in the intertidal zone rather than a direct consequence of inter-specific competition. Ontogenetic changes in diets were observed in two resident species of the assemblage (B. ramosus and G. adustus). The latitudinal trend for herbivory inside this tropical assemblage is discussed in comparison with similar temperate studies in the eastern Pacific.     

Neutral lipid compositions of antarctic fish tissues may reflect use of fatty acyl substrates by catabolic systems

Antarctic fishes contain large quantities of lipid in adipose tissue, blood and oxidative muscle. In this study, the fatty acyl compositions of free fatty acids (FFA) and triacylglycerol (TAG) in serum, adipose tissue and oxidative muscle were determined in two species of Antarctic fishes, Trematomus newnesi Boulenger, 1902, and Notothenia gibberifrons Lönnberg, 1905, collected off the Antarctic Peninsula in February and March 1987. Total lipid contents of serum and oxidative muscle in each species also were measured. T. newnesi, a mesopelagic species, has significantly more lipid in the serum than N. gibberifrons, a demersal species (17.6±2.4 and 10.4±1.0 mg lipid g^-1 serum, respectively). The oxidative muscle of T. newnesi also contains more lipid than does that of N. gibberifrons (12.5 and 9.3% by dry weight, respectively). Fatty acids comprising greater than 5% of one or more of the lipid pools assayed in both species include 14:0, 16:0, 16:1, 16:2, 18:0, 18:1, 20:5 and 22:6. The percentages of 16:1 were lower (p<0.05) in oxidative muscle FFA than in all other assayed lipid pools in both species, suggesting a catabolic preference for some monoenes in oxidative muscle of these fishes. The percentage of 14:0 was two-to three-fold higher in adipose tissue TAG than in all other lipid pools in both species. Differences in fatty acid compositions between lipid pools indicate than proteins involved in the mobilization, transport or catabolism of fatty acids exhibit differential recognition of fatty acids in T. newnesi and N. gibberifrons.     

Predator choice in the field; grouping guppies, Poecilia reticulata, receive more attacks

Capture success of many predator species has been shown to decrease with increasing prey group size and it is therefore suggested that predators should choose to attack stragglers and/or small groups. Predator choice in the laboratory has shown mixed results with some species preferentially attacking large groups and others preferring to attack stragglers over groups. Such predator choices have not been tested in the field. In our study we presented a binary choice between a shoal of guppies and a single guppy to predators in pools in the Arima river, Trinidad. We observed attacks in 11 different pools from a total of 53 predators (20 acara cichlids, Aequidens pulcher, 32 pike cichlids, Crenicichla frenata, and one wolf-fish, Hoplias malabaricus) and found that all predators showed a strong preference for the shoal of guppies in terms of both first choice and total number of attacks. We discuss the implications of these preferences with regards to predator–prey interactions.     

Synergistic effects of ultraviolet radiation and conditions at low tide on egg masses of limpets (<Emphasis Type="Italic">Benhamina obliquata</Emphasis> and <Emphasis Type="Italic">Siphonaria australis</Emphasis>) in New Zealand

The effects of ultraviolet radiation (UVR), desiccation and conditions in tidal pools on embryonic survival were examined for two common pulmonate limpets that lay intertidal benthic egg masses on rocky shores in New Zealand: Benhamina obliquata and Siphonaria australis. Field surveys and manipulative experiments were conducted between December 2006 and September 2007 in the Wellington region of New Zealand (41°17′S, 174°47′E). Egg mass deposition sites in the field were species-specific: B. obliquata deposited eggs primarily in shaded crevices, whereas S. australis predominantly deposited egg masses in the sun and in tidal pools. For both species, however, embryonic mortality was greater in egg masses that had been in full sun compared to shade. For S. australis, there was also high mortality in egg masses in tidal pools or desiccated compared to those that remained submerged in flowing seawater at low tide. In outdoor experiments, embryonic mortality was also always greatest for egg masses exposed to full sun, and lowest for those in shaded treatments. Mortality was also higher if egg masses were in simulated tidal pools, and for S. australis, if desiccated, compared to those submerged in flowing seawater. Periods of particularly sunny conditions with high temperatures also resulted in higher overall mortality. Finally, egg masses of both species that were initially deposited in the shade had greater mortality in response to subsequent UV exposure compared to egg masses initially deposited in full sun. Results from this study suggest that the egg masses of these two species are highly vulnerable to UVR, as well as other intertidal stressors. Embryos of both of these species may be at risk of high mortality particularly during summer when extreme conditions of UV intensity and high temperature coincide with low tide cycles. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Red algae as hosts for endophytic kelp gametophytes

We observed kelp gametophytes endophytic in the cell walls of 17 species of red algae from the San Juan Islands, Washington, USA. Host algae were collected primarily from three sites dominated by different kelp assemblages, including (1) a subtidal site dominated by Agarum fimbriatum Harvey, (2) a second subtidal site dominated by Nereocystis luetkeana (Mertens) Postels et Ruprecht, and (3) a floating dock on which the dominant kelp species were Alaria marginata Postels et Ruprecht, Laminaria groenlandica Rosenvinge, and Costaria costata (C. Agardh) Saunders. Most hosts were filamentous [e.g. Pleonosporium vancouverianum (J. Agardh) J. Agardh, Callithamnion acutum Kylin], or polysiphonous [e.g. Polysiphonia paniculata Montagne, Pterosiphonia dendroidea (Montagne) Falkenberg]; however, similar endophytes were also observed in membranous or bladed red algae [e.g. Membranoptera platyphylla (Setchell et Gardner) Kylin, Polyneura latissima (Harvey) Kylin]. Dozens to hundreds of separate kelp gametophytes were associated with single host thalli. In many cases, the gametophytes developed conspicuous oogonia raised above the thallus surface on characteristic stalks. Presumed zygotes developed through typical embryonic stages into juvenile sporophytes. We argue that the endophytic habit plays an important role in the biology of kelp gametophytes. Received: 5 May 1998 / Accepted: 6 May 1999     

Male care,mate switching,and future reproductive success in a double-brooded passerine

Summary In species with male parental care, polygyny may reduce the parental effort provided by a male, and hence impose a cost on the fitness of his mates, because of decreased growth, survival or health of offspring. I examined a cost of polygyny in the green dart-poison frog, Dendrobates auratus, a species with male parental care in which both male polygyny and mate guarding by females occurs (Summers 1989). All D. auratus males seen carrying tadpoles in a marked area were followed and the pools where they deposited their tadpoles were recorded. Males frequently deposited more than one tadpole in the same pool (in 25% of the observed depositions a male deposited a tadpole in a pool where he had previously deposited at least one other tadpole). Experiments involving manipulation of tadpole densities in pools typically utilized by D. auratus (calabash husks and treeholes) showed that increasing tadpole number had a strong negative effect on both growth rate and survivorship, indicating that polygyny can impose a cost on the fitness of a male's offspring. Hence, females do face a potential cost, in terms of reduced offspring growth and survivorship, when their mates mate polygynously and care for the offspring of other females.     

Decline in metallophytes in tertiary polluted floodplain grasslands in the Netherlands: experimental evidence for metal and nutritional changes in soil as driver factors

Metallophyte vegetation along the River Geul has been almost completely replaced by grasses during the last decades. Field investigations indicated that this was accompanied by higher alkalinity and phosphate availability in the soil, related to the closure of the metal industry and intensification of agricultural practices. An experiment with a full factorial design for phosphate and zinc availability indicated that the metallophytes Silene vulgaris and Thlaspi caerulescens did not grow on zinc-poor soils, irrespective of phosphate availability. The grass Holcus lanatus performed well on phosphate-rich soil, irrespective of zinc availability. An experiment with zinc-poor and zinc-rich floodplain soils confirmed the high zinc demand of the metallophytes T. caerulescens and Armeria maritima and the zinc independence of H. lanatus. A third experiment indicated that a reduced zinc availability due to liming affected only the metallophyte T. caerulescens; it had no effect on the growth of the grass Festuca rubra. This means that increasing alkalinity leads to a decrease in zinc availability, limiting the growth of at least some metallophyte species. An increase in phosphate availability stimulates growth in more competitive fast-growing grasses under zinc-rich as well as zinc-poor conditions.     

Grazing as a measure against grass encroachment in Dutch dry dune grassland: effects on vegetation and soil

A grazing experiment was started in 1984 and 1989 respectively, in two parts of a dune grassland in the nature reserve ‘Zwanenwater’, North Holland; a third part with similar geology and topography was used as a control area and not grazed. An evaluation of the effects of grazing on vegetation patterns, species composition, vegetation structure and humus form was made with the help of vegetation maps from 1986 and 1992 as well as field surveys. Dense tall-grass communities dominated byAmmophila arenaria increased over the period 1986–1992 in the grazed areas, and especially in the non-grazed area (increase in area to 20%, 22% and 50%, respectively). Open communities decreased in the grazed areas, but are still prevalent, while in the ungrazed area they virtually disappeared, with the result that the present percentage areas are 53%, 38% and 17%. Field survey data were classified by TWINSPAN producing four vegetation types. These occur more or less equally in grazed and ungrazed areas, albeit with different percentage areas: (1) open vegetation dominated byCorynephorus canescens; (2) open vegetation characteized, byKoeleria macrantha; (3) heathland dominated byEmpetrum nigrum; and (4) tall-grass communities dominated byAmmophila arenaria. Within a vegetation type, species composition was only marginally affected by grazing regime. Within the open communities the number of species, vegetation height, vegetation cover and soil organic horizons were not affected by grazing. In the tall-grass communities the number of species was significantly larger and the height of the vegetation significantly lower in the area grazed since 1984. In the heathland community the number of species and cover of the moss layer were significantly higher in the 1984 area and ectorganic and endorganic horizons significantly thicker in the ungrazed area. It is suggested that these effects are the result of an increased availability of light, but possibly also of a decreased stock of organic matter and nutrients, due to a decreased input of litter and accelerated rates of decomposition.     

Phosphorus in Phoenix: a budget and spatial representation of phosphorus in an urban ecosystem

As urban environments dominate the landscape, we need to examine how limiting nutrients such as phosphorus (P) cycle in these novel ecosystems. Sustainable management of P resources is necessary to ensure global food security and to minimize freshwater pollution. We used a spatially explicit budget to quantify the pools and fluxes of P in the Greater Phoenix Area in Arizona, USA, using the boundaries of the Central Arizona-Phoenix Long-Term Ecological Research site. Inputs were dominated by direct imports of food and fertilizer for local agriculture, while most outputs were small, including water, crops, and material destined for recycling. Internally, fluxes were dominated by transfers of food and feed from local agriculture and the recycling of human and animal excretion. Spatial correction of P dynamics across the city showed that human density and associated infrastructure, especially asphalt, dominated the distribution of P pools across the landscape. Phosphorus fluxes were dominated by agricultural production, with agricultural soils accumulating P. Human features (infrastructure, technology, and waste management decisions) and biophysical characteristics (soil properties, water fluxes, and storage) mediated P dynamics in Phoenix. P cycling was most notably affected by water management practices that conserve and recycle water, preventing the loss of waterborne P from the ecosystem. P is not intentionally managed, and as a result, changes in land use and demographics, particularly increased urbanization and declining agriculture, may lead to increased losses of P from this system. We suggest that city managers should minimize cross-boundary fluxes of P to the city. Reduced P fluxes may be accomplished through more efficient recycling of waste, therefore decreasing dependence on external nonrenewable P resources and minimizing aquatic pollution. Our spatial approach and consideration of both pools and fluxes across a heterogeneous urban ecosystem increases the utility of nutrient budgets for city managers. Our budget explicitly links processes that affect P cycling across space with the management of other resources (e.g., water). A holistic management strategy that deliberately couples the management of P and other resources should be a priority for cities in achieving urban sustainability.     

Grazing as a measure against grass encroachment in Dutch dry dune grassland: effects on vegetation and soil

A grazing experiment was started in 1984 and 1989 respectively, in two parts of a dune grassland in the nature reserve ‘Zwanenwater’, North Holland; a third part with similar geology and topography was used as a control area and not grazed. An evaluation of the effects of grazing on vegetation patterns, species composition, vegetation structure and humus form was made with the help of vegetation maps from 1986 and 1992 as well as field surveys. Dense tall-grass communities dominated byAmmophila arenaria increased over the period 1986–1992 in the grazed areas, and especially in the non-grazed area (increase in area to 20 %, 22 % and 50 %, respectively). Open communities decreased in the grazed areas, but are still prevalent, while in the ungrazed area they virtually disappeared, with the result that the present percentage areas are 53 %, 38 % and 17 %. Field survey data were classified by TWINSPAN producing four vegetation types. These occur more or less equally in grazed and ungrazed areas, albeit with different percentage areas: (1) open vegetation dominated byCorynephorus canescens; (2) open vegetation characterized byKoeleria macrantha; (3) heathland dominated byEmpetrum nigrum; and (4) tall-grass communities dominated byAmmophila arenaria. Within a vegetation type, species composition was only marginally affected by grazing regime. Within the open communities the number of species, vegetation height, vegetation cover and soil organic horizons were not affected by grazing. In the tall-grass communities the number of species was significantly larger and the height of the vegetation significantly lower in the area grazed since 1984. In the heathland community the number of species and cover of the moss layer were significantly higher in the 1984 area and ectorganic and endorganic horizons significantly thicker in the ungrazed area. It is suggested that these effects are the result of an increased availability of light, but possibly also of a decreased stock of organic matter and nutrients, due to a decreased input of litter and accelerated rates of decomposition. Nomenclature: Van der Meijden et al. (1992) for phanerogams; Corley et al. (1981) for mosses; Grolle (1983) for hepatics.     

Optimal control of lake pH for mercury bioaccumulation control

Mercury is recognized internationally as an important pollutant since mercury and its compounds are persistent, bioaccumulative and toxic, and pose human and ecosystem risks. A critical aspect of mercury cycling is its bioaccumulation, mainly as methylmercury, along the aquatic food web resulting in high risk of human exposure through contaminated fish consumption. Since lake acidity (pH) and mercury methylation are correlated, control of lake pH through lake liming is a possible option to mitigate mercury bioaccumulation. This work proposes to use optimal control theory to derive time-dependent lake liming strategies for a tighter control of lake pH. Since the behavior of the freshwater ecosystems such as lakes is often associated with considerable uncertainties, a robust and realistic analysis should incorporate such uncertainties. This work models the time-dependent uncertain variations in the basic lake pH value and derives the liming profiles in the presence of such seasonal pH fluctuations. Established techniques from real options theory are employed for modeling the uncertainty as a stochastic process, and stochastic optimal control is used for deriving liming profiles. The approach is critically evaluated through applications to various case study lakes. Considering the substantial costs associated with liming operations, the work formulates a multi-objective problem highlighting the tradeoff between accurate pH control and liming cost. The results of the control problem solution are also compared with heuristics based liming. The results, while highlighting the success of using time-dependent liming, put forth certain interesting aspects that might be helpful to a decision maker. The analysis is expected to make liming operation more reliable, thereby presenting one more tool to manage the harmful effects of mercury pollution.