Cassandra James

Spatial variability of the soil seed bank in a heterogeneous ephemeral wetland system in semi-arid Australia

Soil seed banks are an important component of plant community diversity in ephemeral wetlands, allowing many species to persist through unpredictable periods of flood and drought. Spatial variation of extant vegetation in such habitats commonly reflects patterns of flood history and often varies predictably between broadly differing hydro-geomorphic habitat types. Here we investigate whether spatial variation of soil seed banks is similarly controlled by fluvial processes at this scale. Results are presented from a seedling emergence trial using samples collected from a range of habitat types, and at different scales within these, in the ephemeral Narran Lakes system in semi-arid Australia. Composition and structure of soil seed banks varied significantly between habitat types reflecting broad differences in flood frequency. As predicted, germinable seed abundance was found to be highest in intermediately flooded habitats. Variability in soil seed bank composition at a local scale was also found to be influenced by hydrology with greater spatial heterogeneity evident in the river channel as well as amongst the least frequently inundated riparian and floodplain habitats.

Nitrogen driven lakes: The Shropshire and Cheshire Meres?

Chemical and morphological data from eighteen lakes (meres) in the West Midlands, U.K. were examined to determine the relative importance of nitrogen and phosphorus in determining algal biomass. The meres are characterised by high phosphorus concentrations, with mean annual total phosphorus in excess of 300 mug/l. A comparison of indicators of nutrient limitation (absolute nutrient concentrations, nutrient ratios, nutrient enrichment bioassays and heterocyst numbers) sometimes showed contradictory results confirming the necessity for the use of multiple indicators on repeated sampling occasions. Five of the meres showed strong evidence for nitrogen limitation, while two meres showed strong evidence of phosphorus limitation. A number of the meres showed temporal variation in nutrient limitation and were not clearly limited by a single nutrient. We examined the extent to which high phosphorus within epilimnion waters during summer is a function of deoxygenation of the hypolimnion and long water residence times. No relationship was found and we surmise that the high phosphorus concentrations generally found within the meres are the accumulative effects of historic land use.

Empirically derived guidance for social scientists to influence environmental policy

Failure to stem trends of ecological disruption and associated loss of ecosystem services worldwide is partly due to the inadequate integration of the human dimension into environmental decision-making. Decision-makers need knowledge of the human dimension of resource systems and of the social consequences of decision-making if environmental management is to be effective and adaptive. Social scientists have a central role to play, but little guidance exists to help them influence decision-making processes. We distil 348 years of cumulative experience shared by 31 environmental experts across three continents into advice for social scientists seeking to increase their influence in the environmental policy arena. Results focus on the importance of process, engagement, empathy and acumen and reveal the importance of understanding and actively participating in policy processes through co-producing knowledge and building trust. The insights gained during this research might empower a science-driven cultural change in science-policy relations for the routine integration of the human dimension in environmental decision making; ultimately for an improved outlook for earth’s ecosystems and the billions of people that depend on them.

Approaches to Providing and Managing Environmental Flows in China

This paper reviews the course of research on environmental flows in China. It briefly summarizes the history of environmental flows research and introduces twenty approaches used in China to calculate environmental flows. This includes methods adapted from overseas applications and those developed in China to tackle specific environmental issues. The paper gives examples of the implementation of environmental flows in China and identifies some of the deficiencies in environmental flow methodologies. Finally, it discusses obstacles facing the successful implementation of environmental flows in China and suggests the steps required to relieve these impediments.

Water Quality in Chronically Nutrient-Rich Lakes: The Example of the Shropshire-Cheshire Meres

Abstract The Shropshire and Cheshire meres of north-west England are characterised by high phosphorus concentrations. This review assesses the importance of phosphorus and nitrogen concentrations in determining the water and ecological quality of the meres. Palaeolimno—logical evidence indicates that the meres may be naturally eutrophic, but that phosphorus concentrations have increased in the past century. Results show that nitrogen concentrations have also increased and support the hypothesis that high concentrations of nitrogen contribute to reduced macrophyte species richness. In light of the evident significance of nitrogen, the potential role of nitrogen concentrations in driving eutrophication in the meres is discussed.

Zooplankton dynamics from inundation to drying in a complex ephemeral floodplain-wetland

Abstract.Ecological responses to wetting and drying in dryland river floodplain systems are often described in terms of “boom” and “bust”. We suggest that patterns in floodplain species abundances and assemblage structures will be closely linked to the changes in spatial habitat heterogeneity that accompany flooding and drying phases. This study examined the responses of zooplankton through a wetting and drying cycle in a complex floodplain-wetland system in semi-arid Australia, the Narran Lakes. We illustrate the complexity of the zooplankton “boom” and “bust” response. Total densities of zooplankton varied considerably over time and patterns were very dissimilar between sites with abundances varying from <30 animals/L to over 4000 animals/L. We detected different patterns in the proportion of variance in abundances of the broad taxonomic groups (rotifers, cladocerans, ostracods, calanoid copepods, cyclopoid copepods and nauplii) explained by time and space. Site explained the highest proportion of variation in cladoceran and ostracod abundances,whereas variance in calanoid abundances was explained predominantly by time since inundation. Variation in the abundances of the remaining groups was explained largely by the site by time interaction. Zooplankton assemblages were observed to diverge during drying with highest between-site dissimilarities in assemblage structure occurring during the later stages of drying. Such high spatial and temporal variability in zooplankton abundances and community composition could have important consequences for consumers such as fish and some wetland birds that utilize these ephemeral systems for feeding and breeding while they are inundated.

Does stream flow structure woody riparian vegetation in subtropical catchments

Abstract The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA – Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream‐specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are dominated by a diverse array of typical rainforest species, and other factors including broad‐scale climatic gradients and topographic variables have greater influence than hydrology, riparian vegetation is likely to be less responsive to environmental flow management.

Dinophyta Characterise Nitrogen Scarcity More Strongly than Cyanobacteria in Moderately Deep Lakes

A survey of the summer phytoplankton communities of thirty-six moderately-deep north temperate lowland lakes showed that the proportions of Dinophyta and non-heterocyst-bearing cyanobacteria taxa, measured as biovolume, were inversely related to the total nitrogen: total phosphorus (TN:TP) ratio and that these groups were predominant in lakes where available nitrogen fell to undetectable concentrations. The proportion of heterocyst-bearing cyanobacteria was positively correlated to the TN:TP ratio and nitrate. Dinophyta and/or non-heterocystous cyanobacteria were prevalent in lakes with the highest epilimnion nutrient concentrations, whilst heterocystous cyanobacteria predominated in lakes with moderate nutrient concentrations. It is argued that the ability of Dinophyta to migrate vertically and to supplement their nutrient requirements though heterotrophy may enable them to be at least as successful as Cyanobacteria in high nutrient lakes and in overcoming nitrogen-scarcity. Our findings provide evidence that Dinophyta can be used as indicators of water quality.