Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.

/pdf/catastrophic-shifts-in-ecosystems-2yv2mwzdwb.pdf

Catastrophic shifts in ecosystems.

▪ Abstract We review the evidence of regime shifts in terrestrial and aquatic environments in relation to resilience of complex adaptive ecosystems and the functional roles of biological diversity in this context. The evidence reveals that the likelihood of regime shifts may increase when humans reduce resilience by such actions as removing response diversity, removing whole functional groups of species, or removing whole trophic levels; impacting on ecosystems via emissions of waste and pollutants and climate change; and altering the magnitude, frequency, and duration of disturbance regimes. The combined and often synergistic effects of those pressures can make ecosystems more vulnerable to changes that previously could be absorbed. As a consequence, ecosystems may suddenly shift from desired to less desired states in their capacity to generate ecosystem services. Active adaptive management and governance of resilience will be required to sustain desired ecosystem states and transform degraded ecosystems...

/pdf/regime-shifts-resilience-and-biodiversity-in-ecosystem-adn56ypip0.pdf

Regime Shifts, Resilience, and Biodiversity in Ecosystem Management

https://www.owrb.ok.gov/quality/standards/pdf_standards/scenicrivers/Smith,%20Tilman%20and%20Nekola%201999.pdf

Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems

Occasionally, surprisingly large shifts occur in ecosystems. Theory suggests that such shifts can be attributed to alternative stable states. Verifying this diagnosis is important because it implies a radically different view on management options, and on the potential effects of global change on such ecosystems. For instance, it implies that gradual changes in temperature or other factors might have little effect until a threshold is reached at which a large shift occurs that might be difficult to reverse. Strategies to assess whether alternative stable states are present are now converging in fields as disparate as desertification, limnology, oceanography and climatology. Here, we review emerging ways to link theory to observation, and conclude that although, field observations can provide hints of alternative stable states, experiments and models are essential for a good diagnosis.

/pdf/catastrophic-regime-shifts-in-ecosystems-linking-theory-to-4cjnkgwe9s.pdf

Catastrophic regime shifts in ecosystems: linking theory to observation

The turbidity of lakes is generally considered to be a smooth function of their nutrient status. However, recent results suggest that over a range of nutrient concentrations, shallow lakes can have two alternative equilibria: a clear state dominated by aquatic vegetation, and a turbid state characterized by high algal biomass. This bi-stability has important implications for the possibilities of restoring eutrophied shallow lakes. Nutrient reduction alone may have little impact on water clarity, but an ecosystem disturbance like foodweb manipulation can bring the lake back to a stable clear state. We discuss the reasons why alternative equilibria are theoretically expected in shallow lakes, review evidence from the field and evaluate recent applications of this insight in lake management.

Alternative equilibria in shallow lakes

Biomanipulation (as defined by Shapiro) and top-down or consumer controlled forces refer to the control of natural aquatic organisms to improve water quality instead of through nutrient management. A cornerstone of biomanipulation studies was established during the late fifties and early sixties when the effect of fish on water quality via zooplankton predation was shown. Biomanipulation through animals other than fish or zooplankton has also been noted. The classicallimnological concept of lake trophodynamics goes from nutrients through phytoplankton to zooplankton and fish. Therefore, top-down forces as a potential tool for manipulation was seen as a pioneering approach. During the seventies, many studies on trophic cascading effects of fish through zooplankton predation on phytoplankton have been carried out. The removal of Macrophytes by grass carp has also been investigated and was implemented as a practical way of controlling these plants. During the eighties the concept of biomanipulation was broadened to include other aspects of the complex interactions between food-web components such as the different nutrient flux pathways. In order to be able to make long term predictions for water quality improvement in lakes and reservoirs, the combined analysis of both top-down and bottom-up forces is required.

Biomanipulation - Tool for water management.

The current state of biomanipulation was the subject of muchdiscussion at Shallow Lakes ‘95. This led to a workshop focusing onthe factors influencing the establishment of macrophytes and themechanisms responsible for their stability followingbiomanipulation. The purpose of the current paper is to distilcurrent knowledge on biomanipulation in shallow lakes gleaned fromdiscussions at the conference and recent literature.Biomanipulation should be used in the theoretical context of twoaltemative stable equilibria, as the extreme perturbation requiredto move from a phytoplankton dominated state to one dominated bymacrophytes. Understanding the nature of the factors and mechanismsresponsible for turbid water, is critical if biomanipulation is tobe appropriate. We suggest that with sufficient information,particular components of the fish community may be targeted andprecise figures for removal, designed to exceed critical thresholdvalues, may be set. Without this knowledge, a ‘play-safe’ strategyshould be adopted and at least 75% of the fish removed. Stockingwith piscivores may be a useful additional measure to fish removal.The principal objective of biomanipulation in shallow lakes is togenerate a period of clear water of sufficient length to allowmacrophytes to establish. To this aim, as well as for technicalreasons, biomanipulation is best undertaken in winter and earlyspring to generate clear water as early as possible in the season.In the cases where grazing is important, this coincides with thespring peak of Daphnia spp. Biomanipulation may have to berepeated if macrophytes do not colonise effectively within thefirst season. The factors responsible for the lag in response ofmacrophytes in some cases and the potential mechanisms contributingto the maintenance of clear water in macrophyte beds are discussed.From empirical data sets from many lakes, both a relative increasein the piscivorous fish stock and a reduction in nutrient levelsare thought to be important in stabilising the system in thelong-term. Whether biomanipulation may lead to alternativeequilibria (i.e. high diversity macrophyte communities withpiscivorous fish at high P) is unknown. Further study ofexceptional cases, theoretical modelling and development andanalysis of more long-term (>10 years) case histories isrecommended.

Biomanipulation in shallow lakes: state of the art

The effects of fish stock reduction have been studied in 3 Dutch lakes (Lake Zwemlust, Lake Bleiswijkse Zoom and Lake Noorddiep) and 1 Danish lake (Lake Vaeng) during 4–5 years. A general response is described. The fish stock reduction led in general to a low fish stock, low chlorophyll-a, high Secchi-disc transparency and high abundance of macrophytes. Large Daphnia became abundant, but their density decreased, due to food limitation and predation by fish. The total nitrogen concentration became low due to N-uptake by macrophytes and enhanced denitrification. In Lake Bleiswijkse Zoom the water transparency deteriorated and the clear water state was not stable. The fish stock increased and the production of young fish in summer was high. Clear water occurred only in spring. Large daphnids were absent in summer and the macrophytes decreased.

/pdf/long-term-responses-to-fish-stock-reduction-in-small-shallow-qabw6ccvc3.pdf

Long-term responses to fish-stock reduction in small shallow lakes: interpretation of five-year results of four biomanipulation cases in The Netherlands and Denmark

Vegetated areas with clear water in turbid shallow lakes

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