Biodiversity, fish ponds and agricultural land use in the cultural landscapes of the Dombes area, France

Vanacker, M., Wezel, A., Payet, V., Robin, J. (2015). Determining tipping points in aquatic ecosystems: the case of biodiversity and chlorophyll a relations in fish pond systems. Ecological Indicators 52: 184–193.
The management of biodiversity in aquatic ecosystems requires knowing the state of water quality linked to regime shifts in various taxonomic groups. We examine this question by studying the fish ponds in the Dombes region, France. These waterbodies are characterized by a high diversity of species. High levels of nutrients due to certain fish farming practices may cause significant eutrophication leading to loss in biodiversity and a shift from high coverage of aquatic vegetation to phytoplankton dominance may also be observed. The aim of this study is to assess tipping points, thresholds for effect, along a gradient of chlorophyll a in different taxonomic groups: aquatic vascular plants, phytoplankton, dragonflies and aquatic macro-invertebrates. Tipping points are analyzed with three different statistical methods: a method which evaluates tipping points with a difference in the mean (TMEAN), a second method which evaluates tipping point by comparing the mean and linear regressions before and after the tipping point (FSTAT) and third a method which evaluates linear regressions with a pivotal tipping point (SEGMENTED). We also compare tipping points for the different taxonomic groups using five different diversity indices: Observed richness, Jackknife first order, Fisher’s alpha, Simpson index and Evenness.
Our results show that there is an important variation in tipping points following the three statistical methods, but the SEGMENTED is the best method for evaluating tipping points. We observe a high difference of tipping point values for the different taxonomic groups depending on the diversity indices used. Jackknife first order has a better performance to evaluate a eutrophic change according to the diversity than the other indices.
In all taxonomic groups, aquatic vascular plants are the most impacted by the chlorophyll a and almost all their tipping points are observed around 60 µg/L chlorophyll a concentrations. No significant relationship is found between chlorophyll a and phytoplankton diversity, while the two other groups, dragonflies and macro-invertebrates, are both impacted by the chlorophyll a but their relevant tipping points are situated in higher values than aquatic vascular plants.

Robin J., Wezel A., Bornette G., Oertli B., Arthaud F., Pobel D., Rosset V., Angélibert S., Vallod D. (2014). Biodiversity in eutrophicated shallow lakes: determination of tipping points and tools for monitoring. Hydrobiologia 723: 63-75.

Rosset V., Angélibert S., Arthaud F., Bornette, G., Robin, J., Wezel, A., Vallod D., Oertli B. (2014). Is eutrophication really a major impairment for small waterbody biodiversity? Journal of Applied Ecology 51 (2): 415–25.

Wezel, A., Arthaud, F., Dufloux, C., Renoud, F., Vallod, D., Robin, J., Sarrazin, B. (2013). Varied impact of land use on water and sediment parameters on fish ponds of the Dombes agroecosystem, France. Hydrological Science Journal 58 (4): 1–17.
Agricultural land use in the area of water bodies is generally considered to increase the nutrient status of the water body water and sediments. But is this also the case for already nutrient-rich fish ponds? We studied 83 fish ponds in the Dombes region, France, where 1100 ponds are located in a heterogeneous agricultural landscape. Different water and sediment parameters were analysed for ponds and in ditches after rainfall events. Land use was studied in the primary catchment of ponds and in a 100-m zone around ponds. Soil parameters of different land-use types were analysed and farmers interviewed about agricultural practices. Increasing cropping area in the catchment of the ponds is significantly correlated to higher PO43- concentration of pond water, and to a lower degree also to NO3-, but only in certain years with higher rainfall and with a more uneven distribution in spring. Sediment parameters were not significantly influenced. High NO3- concentration in the water of a ditch during significant rainfall events was found for a cropland dominated catchment.

Wezel, A., Chazoule, C., Vallod, D. (2013). Using biodiversity to valorise local food products. The case of fish ponds in a cultural landscape, their biodiversity and carp production. Aquaculture International 21 (6): 1395–1408.
Today we need to produce sufficient food and simultaneously conserve biodiversity. But, could biodiversity associated with certain food production practices also be used in marketing products? We analyse this possibility for creating a food quality label for carp raised in the Dombes territory, a cultural landscape of fish ponds in France. The biodiversity of 99 fish ponds was studied in the Dombes territory by analysing aquatic vegetation, dragonflies, amphibians, marcoinvertebrates, habitats around ponds, and water quality. In addition, a survey with 200 questionnaires and interviews was conducted with consumers to investigate fish and carp consumption, and knowledge about quality labels and biodiversity. Findings reveal that fish production practices conserve remarkable species diversity, particularly for aquatic vegetation, dragonflies and amphibians, and habitats around the ponds. This relatively high level of biodiversity is found in spite of having very nutrient-rich fish pond systems, systems for which normally a low level of biodiversity is expected. Nevertheless, currently this biodiversity cannot be valorised for setting up a quality label for locally produced carp. Firstly, few consumers have adequate knowledge about carp and are interested in eating it. Secondly, most of them have less knowledge about the quality label which wanted to be established for carp from the Dombes. Thirdly, only less than one-third of the consumer is familiar with the term biodiversity. Fourthly, the stakeholder network of the supply chain is presently not able to communicate the message of biodiversity as they themselves lack a sufficient knowledge about biodiversity of their systems.

Wezel, A., Guerin, M., Robin, J., Arthaud, F., Vallod, D. (2013). Management effects on water quality, sediments and fish production in extensive fish ponds in the Dombes region, France. Limnologica 43 (3): 210-218.
In aquaculture, management practices such as supplementary feeding or fertilisation of water are generally considered to improve fish yield in ponds or shallow lakes. Nevertheless, in semi-natural systems where many ponds or lakes are situated in a cultural landscape, this is much less evident for certain fish farmers because fish production systems are often quite extensive, and fish production is only one economic activity among others for these fish farmers. In this paper we analyse the influence of different management practices on fish yield and nutrient status of fish ponds’ water and sediments, and we have an additional regard on potential implications of this in the perspective of the European Water Framework Directive. This directive demands that artificial water bodies such as fish ponds have to attain a good ecological potential in 2015, and thus to adapt water body management to achieve this. In total, 83 fish ponds were studied from 2007 to 2009 in the Dombes region, France. This region is characterised by 1100 nutrient rich fish ponds located in a heterogeneous agricultural landscape with cropping, animal husbandry and forestry. Different water parameters (PO4, NO3, total P, total N, NH4+, Chlorophyll-a) were analysed from April to October in each year. Sediments were sampled in March and October and analysed for available P, total N, organic matter and Ca concentration. Data about pond management practices such as fertilisation of pond water, supplementary feeding as well as fertilisation and liming of pond grounds when they are emptied and let dried out during a year, and harvested fish were collected by interviewing pond owners and pond managers. The main results found are that the combination of the annual management practices supplementary feeding and fertilisation, increased significantly the fish yields. When combining the annual with the non-annual management practices fertilisation of pond grounds and liming of pond grounds during a year when ponds are emptied, highest yield were obtained. Using only the non-annual practices, yields could be positively influenced. Lowest yields were found when no management practice was applied. Significant, but contrasting effects of pond management practices on water or sediment parameters were only found for available P of sediments and NO3- for the management practices supplementary feeding, fertilisation of water, or liming of the pond ground. Whereas available P of sediments showed higher values with the three practices, NO3 in the water showed lower values. Although only few significant differences were found, means of parameters showed a certain trend as they were in many cases, besides for total N and NO3, higher with the management practice. Our results show that there is a limited effect of pond management practices on the chemical status of the pond water and sediments. This also suggests a limited potential to change management practices to respond to the demand of the European Water Framework Directive for good water quality and ecological potential.

Arthaud F., Mousset M., Vallod D., Robin J., Wezel A., Bornette G. (2012): Effect of light stress from phytoplankton on the relationship between aquatic vegetation and the propagule bank in shallow lakes. Freshwater Biology 57: 666–675.
1. The way light stress controls the recruitment of aquatic plants (phanerogams and charophytes)
is a key process controlling plant biodiversity, although still poorly understood. Our aim was to investigate how light stress induced by phytoplankton, that is, independent from the aquatic plants themselves, determines the recruitment and establishment of plant species from the propagule bank. The hypotheses were that an increase in light stress (i) decreases abundance and species richness both of established aquatic plants and of propagules in the bank and (ii) decreases the recruitment success of plants from this bank.
2. These hypotheses were tested in 25 shallow lakes representing a light stress gradient, by sampling propagule banks before the recruitment phase and when the lakes are devoid of actively growing plants (i.e. at the end of winter), established vegetation at the beginning of the summer and phytoplankton biomass (chlorophyll a) during the recruitment and establishment phase.
3. The phytoplankton biomass was negatively correlated with the richness and abundance of established vegetation but was not correlated with the propagule bank (neither species richness nor propagule abundance). The similarity between the propagule bank and established vegetation decreased significantly with increasing phytoplankton biomass.
4. The contrast in species composition between the vegetation and the propagule bank at the highest light stress suggests poor recruitment from the propagule bank but prompts questions about its origin. It could result from dispersal of propagules from neighbouring systems. Propagules could also originate from a persistent propagule bank formerly produced in the lake, suggesting strong year-to-year variation in light stress and, as a consequence, in recruitment and reproductive success of plants.

Arthaud F., Vallod D., Wezel A., Robin J., Bornette G. (2013). Short–term succession of aquatic plant species richness along ecosystem productivity and dispersal gradients in shallow lakes. Journal of Vegetation Science 24 (1): 148–156.
Questions: The highest species richness is usually expected at an intermediate stage of development since the last major disturbance event, but some studies have shown that ecosystem productivity and dispersal may modify this pattern, suggesting the need for further studies on the effects of productivity and dispersal
on the dynamics of species richness through succession. In this study, we analysed aquatic plant species richness in relation to (1) succession stage, measured as numbers of years since the last disturbance that affected the ecosystems; (2) lake productivity, measured as the chlorophyll a concentration; and (3) connectivity to similar nearby ecosystems, a proxy for the potential input of diaspores.
Location: Shallow lakes of the Dombes region, France.
Methods: Every 5–7 yr these shallow lakes are emptied and left to dry out for 1 yr. These drought disturbances lead to complete destruction of the submerged aquatic plant communities. Sixty lakes arranged along a gradient of productivity were selected. The probability of diaspore input was considered to increase from upstream to downstream, as lakes are organized in hydrologically connected networks via ditches, through which the downstream lakes receive water from the upstream lakes. For each lake, the aquatic plant species richness (from systematic summer vegetation sampling), time since the last disturbance (last summer drying),
productivity (estimated as chlorophyll a concentration) and probability of diaspore input (assessed fromposition in the network) were recorded.
Results: The aquatic plant species richness decreased with the time since the last disturbance for all of the lakes, but there was a significant interaction with the chlorophyll a concentration and position of the lake in the network. At the lowest ecosystem productivities, the relationship between successional stage and species richness was hump-shaped, whereas the species richness decreased with increasing time since the last disturbance when productivity increased. The lake’s position in the network did not influence species richness during the first 2 yr after
disturbance, but from year 3 and thereafter, lakes connected to high numbers of upstream lakes consistently exhibited decreased richness, contradicting the expected trend of increasing species richness with increasing diaspore inputs.
Conclusions: This study indicates that both ecosystem productivity and connectivity strongly affected the relationship between aquatic plant species richness and succession, and that these factors should be taken into account in further developments of the intermediate disturbance hypothesis.

The region and agricultural land use
The Dombes region in France is characterised by about 1100 ponds (about 11 000 ha) located in an agricultural area with pastures, cropped fields and forests. The fish farming practiced in the ponds is oriented toward raising mainly carp, but also pike. This activity emerged already in the medieval period because of the need to find fish at a time in which food prescriptions were very strict. Today it is based on an extensive system that alternates fish farming and grain farming on the same unit of land. This particular form of crop rotation generates a complex set of technical and cultural practices that increases biodiversity by conserving, in particular, a great number of wild animal and plant species in the ponds and around them. The great diversity in using the ponds environment not only for fishing and farming, but also for hunting determine the functioning of these cultivated ponds. In addition, the Dombes carpe production is presently considered for receiving a protected geographical indication label, thus potentially increasing the value of local production for marketing.