Impacts of water scarcity and drought on Iberian aquatic ecosystems

Transcription

1 Impacts of water scarcity and drought on Iberian aquatic ecosystems Dr. Carles Ibáñez Martí, Director of the Aquatic Ecosystems Program, IRTA International Drought Symposium, UC Riverside, March 2010

2 Content - Some concepts... - Impacts of water scarcity on continental aquatic ecosystems. - Responses and adaptations in Iberian aquatic ecosystems. - Some examples from rivers, estuaries and wetlands. - Conclusions and recommendations.

3 Drought, water scarcity, overexploitation, efficiency Drought: natural, temporal and cyclic reduction of water resources in terrestrial or aquatic ecosystems. Water scarcity: natural or human-induced reduction trend of water resources in ecosystems or human systems. Droughts are superimposed to water availability trends. Overexploitation: human use of water resources beyond its limit of regeneration or availability, leading to an unsustainable scenario. Water stress (or deficit) can be due to a combination of natural drought, water scarcity (i.e., climate change) and overexploitation. Efficiency: optimal use of water resources per unit of human use. Efficiency does not necessarily imply sustainability (i.e., we can efficiently dry the Amazon River).

4 Pressures, impacts, responses, adaptations Pressures: consequences of human activities that may affect the environment (i.e., water abstraction, damming, global warming, overfishing, etc.). Impacts: measurable effects of human pressures on the environment (i.e., loss of water quality, detrimental effects on species, sediment retention, etc.). One pressure may (or may not) have one or more impacts. Responses: short-term changes of the system due to one or more impacts (i.e., changes in key species, higher mortality rate, increased erosion, etc.). Adaptations: longer-term trends of the system, involving more structural and permanent changes (i.e., changes in the food web, changes in the life strategy of species, ecosystem regime shifts, changes in species composition, etc.). Ecosystems and species may or may no adapt to new stressing and changing conditions. Solutions: whatever helps to solve the problems.

5 What is the problem? Problem: increasing exploitation of water resources, leading to increasing water scarcity. This problem is exacerbated during drought periods. Pressures: irrigation, urban water demand, land use changes, climate change, drought, etc. Impacts: flow regime, water level, sediment dynamics, water characteristics, biodiversity loss, etc. Responses: changes in key species, higher mortality rate, higher success of invasive species, etc. Adaptations: changes in the food web, changes in the life strategy of species, ecosystem regime shifts, changes in species composition, etc. Efficiency: yes, in Spain we are quite efficiently drying up most of rivers and aquifers... Solutions: establish limits in the use of water resources (carrying capacity), with a consumption rate well below the resource availability (environmental flows, strategic underground reserves, etc.).

6 Responses of aquatic ecosystems to drought and scarcity Abiotic responses: - Reduced water flow and/or water level; reduced surface. - Changes in water temperature, mineralization and other physico-chemical variables. - Changes in substrate structure and/or composition. - Changes in sediment concentration and/or transport. - Oxidation/decomposition of the organic matter. - Compaction/subsidence of the soil.

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8 Biotic responses to decreased flow or water level Changes in macroinvertebrate assemblage composition in a stepped fashion during transitions across threshold discharges or water levels (Source: Boulton 2003). During drying, total numbers of taxa are posited to decline sharply when submerged or trailing littoral vegetation is isolated from the free water (1 to 2), then as flow ceases in the riffle (2 to 3), and when surface water disappears (3 to 4). Plausibly, further declines occur in the hyporheic zone as subsurface water levels fall.

9 Effects of drought on fishes Numbers of studies showing specified effects of drought on fishes, summarized from 50 previously published papers (Source: Matthews and Marsh-Matthews 2003). Solid bar, effect found by original authors or accepted as valid; open bar, speculative or unconfirmed; hatched bar, effect tested for but did not found significant by original authors.

10 The flow regime is a key factor Principle 1 Flow is a major determinant of physical habitat in streams, which in turn is a major determinant of biotic composition. Principle 2 Aquatic species have evolved life history strategies primarily in direct response to the natural flow regimes. Principle 3 Maintenance of natural patterns of longitudinal and lateral connectivity is essential to the viability of populations of many riverine species. Principle 4 The invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. Guiding principles about the influence of flow regimes on aquatic biodiversity, as formulated by Bunn and Arthington (2002).

11 Solutions: environmental flows - The most important measure to avoid the rapid deterioration of the Iberian aquatic ecosystems is to determine and implement an environmental flow regime. - The methodology to determine the flow regime must be hydrologically based on the natural flow regime, and ecologically based on the key biological processes, in order to maintain the health and integrity of the system. - Establishing environmental flows is like limiting greenhouse emissions to solve the climate change problem, both are measures directed to put limits to the consume of resources. This is why this issue is so difficult and conflicting (and so important), because it goes at the root of the problem, the limitation of resources.

12 Responses of Iberian aquatic ecosystems The main responses of Iberian aquatic ecosystems to drought and increased water stress are reported to be: Changes in biotic community structure Changes in habitat availability Alteration of ecosystem metabolism Increase of eurytolerant and invasive species Increase of pollution Reduced resilience against global change impacts

13 Responses of Iberian rivers River flow reduction and success of invasive species: ( a ) Observed Predicted values % cases well values 0 1 predicted Multivariete logistic regression. Velocity was the only significant variable Simulated with HEC-RAS and validated with field data (b ) Relationship between flow conditions and fish assemblage structure in the lower Ebro River: a) relationship between river flow and water velocity; b) probability of finding a fish assemblage dominated by native species as predicted by logistic regression (0 = > 50% introduced species; 1 = >50% native species).

14 Responses of Iberian estuaries and deltas: the Ebro Delta Increasing soil salinity affecting crops Decreasing river flow and sediments Coastal retreat of 10 m/yr Organic matter decomposition Salt wedge intrusion 30 Km uptream

15 Responses of Iberian wetlands: the case of Daimiel 'Don Quixote park' destroyed by exploitation One of the world's great natural wonders which provided the back drop to Don Quixote's adventures through central Spain has been destroyed by fire and the theft of water. By Edward Owen in Madrid Published: 3:19PM BST 22 Oct 2009 TelegraphNews A boat is seen in a wetland gone dry in Las Tablas de Daimiel National Park, in Castilla-La Mancha, Spain Photo: AP

16 Spanish wetlands shrouded in smoke as overfarming dries out peat National park which was once a 'paradise' now on fire and churning out tonnes of CO2 Giles Tremlett, Las Tablas de Daimiel, central Spain guardian.co.uk, Monday 19 October BST

17 Spain begins to flood dried out national park that had underground peat fire HAROLD HECKLE Associated Press Writer January 11, :57 a.m. Los Angeles Times, January 18, 2010 In this Oct. 13, 2009 file photo, a boat is seen in a wetland gone dry in Las Tablas de Daimiel National Park, in Castilla-La Mancha, Spain. The government has begun flooding an environmentally valuable expanse of Spanish wetland that dried up through mismanagement of water resources in a bid to save it from an underground peat fire, it was reported on Sunday Jan. 10, (AP Photo/Arturo Rodriguez, File) (Arturo Rodriguez, AP / October 13, 2009)

18 And then, climate change arrived Past trend in air temperature in the lower Ebro basin (Tortosa) Temperatura mitjana màxima anual T=0.028*Any Temperatura mitjana anual T=0.017*Any Temperatura mitjana mínima anual T=0.007*Any Temperatura (ºC) Any

19 Expected climate change impacts on water runoff by the end of the century (blue denotes relative increase, red denotes relative decrease, in percentages). Mean change of annual runoff in percentage between present ( ) and (IPPC SRES A1B emissions scenario). Source: IPCC 4AR, 2007

20 Climate change in Europe and the Iberian Peninsula These maps illustrate what can be expected in Europe by the end of the century, according to the IPCC scenario (SRES A2) whereby no action is taken to reduce greenhouse gas emissions, so that the global mean temperature increases by about 3.4 C by the 2080s compared to 1990 levels. Under this scenario, nearly all European regions are expected to be negatively affected and up to half of Europe s plant species could be vulnerable or threatened by 2080 (Source: PESETA Project, European Union).

21 Simulated extinction of plants by 2080s - (a) local (b) averaged by biogeographical region Source: EC co-funded project ATEAM, Final Report, 2004

22 Conclusions and recommendations First limits, then efficiency - The Mediterranean aquatic ecosystems of the Iberian Peninsula are adapted to cyclical drought under natural conditions, but at present they are severely impacted by water scarcity due to overexploitation of water resources. - This situation will be aggravated by the increasing effects of climate change, since the Mediterranean is going to be one of the most impacted regions worldwide, and all the reported impacts are negative and strong (Tº, rainfall, crop yield, biodiversity loss, etc.). - Consequently, the water policy must quickly shift towards a demand-management and ecosystemic oriented approach, in order to reduce the total water use, increase the water efficiency and restore the aquatic ecosystems. - One of the main measures to be urgently implemented for mitigating the effects of water scarcity in Mediterranean aquatic ecosystems is the establishment and implementation of a pulsing environmental flow regime, incorporating both minimum and maximum flows designed to maintain the crucial ecological functions and the biodiversity. - Another important measure is the restoration of the aquatic habitats, especially the partial recovery of the hydrological and ecological connectivity that has been severely reduced by the construction of dams and other infrastructures; in this sense, the recovery of the sediment flow and the transit of fish through the reservoirs by means of appropriate bypass systems should be a priority. - Future research should focus on quantifying the ecological effects of water scarcity at different spatial and temporal scales, developing specific ecological indicators of water stress, and also on determining and modeling the influence of environmental flows in maintaining biodiversity and ecosystem functions and services.