95 research outputs found
Use of open-top chambers to study the effect of climate change in aquatic ecosystems
The aim of this research was to explore the possibility to use inexpensive open-top chambers (OTCs) as passive artificial warming devices in experimental aquatic studies. Our results show that OTCs give a significant temperature increase compared with the control. The measured increase (up to an average of 2.3°C) corresponds with predicted climatic warming. Due to their open top, the light quantity and quality is only minimally reduced. We found that OTCs are especially suited for studying the effect of climate change in small waters as the vertical temperature gradients remain unchanged. They can also easily be transported to remote environments. We discuss other advantages and disadvantages of these devices for aquatic studies and compare them with other warming devices
Climate change and bathing water quality
In the new European bathing water directive, 2006/7/EG, two microbiological indicators, i.e. intestinal enterococci and Escherichia coli, are used to assess the state of the official outdoor bathing waters. In this directive also cyanobacteria are included, being a cause of insufficient bathing water quality. Climate change will affect bathing water quality with respect to both the number of pathogens and cyanobacteria, as well as their impact on human health. It is to be expected that by 2050, compared to 1990, the winters in The Netherlands will be milder and wetter, the summers will be warmer, with less frequent, but more intensive showers, thus increasing the chance for flooding and the growing season will be longer. It is most probable that these changes in climate will have effects on the health risk for bathing in surface waters. Therefore, a literature study was made to investigate the impact of climate change on bathing water quality and the applicability of the new European bathing water directive for The Netherland
Biological assessment of effects of combined sewer overflows and storm water discharges.
The biological effects of discharges from combined or separated sewer systems are difficult to assess or to predict due to variahilities in concentrations, environmental conditions, morphometry, susceptibility of organisms, seasonality and other factors. A general discussion of the problem results in an outline of two approaches. The first approach is to generalize field experiences and some examples of results are presented and explained. Notably site-specific conditions are shown to overshadow effects of discharges for many of the biological components in the ecosystem. The secend approach is to perform toxicity tests which account for the temporal and spatial scales encountered in the field and for the relevant concentratien levels
EUPHRESCO – DeCLAIM: a decision support system, for control of alien invasive macrophytes
This report contains the result of a research programme on four invasive aquatic macrophytes,
Cabomba caroliniana (Fanwort), Hydrocotyle ranunculoides (Floating pennywort) , Myriophyllum
aquaticum (Parrott’s feather) and Ludwigia grandiflora (Water primrose). The collaborative project
was intended to generate a prototype decision support system for optimising control measures for
these species, considered to be the four most troublesome invasive alien aquatic weeds at present
in the UK and NL. A further reason for selecting these species is that they are widely sold in the
horticultural trade and are therefore the number of invaded sites is likely to increase in the short
term.
C. caroliniana, was selected as a representative of the Myriophyllids growth form, representing 35%
of the import volume of aquarium plants in The Netherlands. In 2009 it is found at three sites in The
Netherlands, posing serious problems at one. It has been present at two sites in the UK recent past
and was collected from one site again in autumn 2011.
H. ranunculoides, was selected as a representative of the Stratiotids s.l. growth form, is at present
the most troublesome invasive alien aquatic weed in the United Kingdom and The Netherlands, and
is showing increased distribution in neighbouring countries, including Belgium and Germany as well
as in Australia, Uganda and Zimbabwe.
A second representative of the Stratiotids s.l. growth form, L. grandiflora, has proven to have a
severe detrimental ecological impact in France and is gaining importance in The Netherlands. In the
UK promising management strategies have already been developed using and the infestation in the
wild has responded well to rapid application fo control measures.
The third representative of the Stratiotids s.l growth form is M. aquaticum. This species has been
sold extensively by the aquatic nursery trade as an ornamental species for domestic ponds. It is now
present in many natural lowland static water sites in the UK. The species is still very popular in The
Netherlands, and the number of occurrences is increasing.
The project was divided into several work packages in order to prioritise the order in which data were
derived and used in the project. The first stage was to collect all published data on the individual
species, in order to gain information on various physiological parameters of the species to put into
the model CHARISMA, a model that predicts biomass of a species given both physiological and
environmental data. We found that although the species were relatively common in the UK and the
Netherlands, data on physiology were not widely available and we had to estimate some of the more
important model parameters to get a realistic output. This is an area of possible experimental error
and can only be corrected by actual field and laboratory measurements on net photosynthetic rate,
light compensation point, biomass production related to nutrient availability and other indices,
including shoot to root ratios, leaf area indices etc.. The literature survey also provided information
on the native range of the species from which we were able to derive optimum environmental
conditions for growth in Europe and the effect of any management techniques already in use. The
literature survey also produced information on the main reproductive strategies, either by vegetative
means such as fragmentation, or by seed production, or a combination of both. Most species have
very effective reproductive strategies using vegetative fragmentation and seed production in both
countries was considered to be relatively unimportant.
Stage two of the project involved an assessment of the areas at risk of colonisation by the four
species in both countries. For the Netherlands it was assumed that if the site of an occurrence
shared both physical and chemical characteristics, then it should be classed as at risk. The low
altitudes and low slopes of most watercourses in the Netherlands create a situation in which the
whole country can be considered at risk. For the UK, we used the elevation data for known
occurrence and plotted an area at risk based on this altitude plus 100m, to account for any unknown sites. This produced different maps for each species as some had been found at higher altitudes
than others. We do not consider this to be as accurate as possible and the integration of
temperature data, especially a day degree index could improve the prediction of at risk areas for
each species in the UK. This is an important topic for inclusion in future work.
The third area of work was to assess current methods of control and to develop or optimise new
techniques. This was carried out in conjunction between all four project partners. Considerable
improvements in the management of C. caroliniana were made during this project and have been
implemented by water boards in the Netherlands. A consistent approach to management of H.
ranunculoides has been adopted in this project and the approaches to management of the two other
species have been shown to be effective in the current regulatory conditions.
The spatially explicit model CHARISMA was developed for two native macrophytes species in the
Netherlands and was used in this project to model growth and biomass accumulation of the four nonnative
invasive macrophyte species. Some of the input parameters used in the original model were
not valid for the new species, and estimates or adjustments had to be made. However, for three out
of four of the new species, the predictions of biomass and dominance were quite accurate and the
model could be developed for these species without excessive modification. The only species that
did not comply well with the model was C. caroliniana, but only in the degree of overwintering
biomass required for dominance in the following season. This is probably due to a lack of any data
for physiological characteristics of this species in winter in Europe and this data gap should be
addressed for this species and others in order to accurately model the behaviour of other species in
European conditions.
The main objective of this project was to produce a draft Decision Support System that could be
used by field operatives and office based managers to identify the species accurately, and to enable
a rapid risk assessment to be made in the field that could be reported in a consistent manner,
enabling a rapid response to be made against the species with the aim of preventing further spread
and eventually eradication the species from the affected watercourse. In order to make the response
to aquatic non-native species consistent and proportionate a pictorial field and office guide has been
produced that provides descriptive photographs of characteristic features, areas at risk, typical
habitat types, and available management techniques. We have deliberately left out costs of
management as these vary within each country and certainly between countries. In addition, each
species chapter will be made available at www.declaim.eu . The DSS was submitted to the Non
Native Species Secretariat in the UK for comment before being used by managers. In the
Netherlands the DSS was submitted to representatives of various water boards that are actively
involved in trials to control invasive macrophytes. The comments received were positive and helpful
and led to developments in the current version
Eutrofiering in Nederland.
Een derde onderzoek is uitgevoerd naar de eutrofieringstoestand in de (semi-) stagnante zoete oppervlaktewateren in ons land. Van 121 plassen en meren werden min of meer volledige gegevens ontvangen betreffende de fysische, chemische en biologische kenmerke
Young mangrove stands produce a large and high quality litter input to aquatic systems
Mangrove swamps are key ecosystems along the Vietnam coast. Although mangrove litter is thought to represent an important input of organic matter and nutrients to the coastal aquatic systems, the factors determining the quality and size of this litter flux have not been studied so far. We monitored leaf, stipule, twig, and reproductive litter monthly in monocultures of Rhizophora apiculata mangrove forests of 7, 11, 17 and 24 years old in the Camau province, Mekong Delta, Vietnam. Litter traps were used to measure litter fall production from June 2001 till May 2002. Total litter fall was in the range of 8.86-14.16 t DW ha-1 year-1. Leaves were the main component, and represented 70% of litter fall production in all stands. Total litter fall was lower in the older stands but the amount of reproductive litter was significantly higher in these stands (17 and 24 years). Biomass of leaf litter was highest between the end of the wet season and the beginning of the dry season. Phosphorus and nitrogen levels in leaf litter were significantly higher in younger than in older stands. Overall, our study indicated that young stands produced the highest input of litter and particularly of nitrogen and phosphorus to the surrounding aquatic system. Consequently, these stands contribute significantly to the fisherie
Some structural characteristics of the phytoplankton in the Oude Waal near Nijmegen, The Netherlands
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