Summary

Preliminary Findings - A Summary of the 2001 Survey

This survey provides important base-line information for the freshwater sites of the Falkland Islands in 2001 and, although full results of water quality and biological characteristics are not yet available, some of the preliminary results and initial observations can be summarised. However, perhaps the principle point to make is that the base-line characterization of 28 Falkland Island sites has established reference conditions that can not only allow sites to be classified and evaluated but also allow comparison with future environmental change assessments of water quality and aquatic biology.

In this summary, four aspects are dealt with (i) the range of site types and water quality (ii) biodiversity issues (iii) environmental change and historical perspectives (palaeolimnology) (iv) some implications and prospects for further work.

Site typology: Most of the standing freshwater bodies on the Falklands are shallow and do not exceed about 2 m depth. Only the upland tarns exceed this depth and Mt. Adam Tarn is probably the deepest site on the Island at 16 m maximum depth. Of the lowland sites, these were either brown water pools in peaty soils and were either underlain by peaty sediment (Mutton Pond, Wireless Ridge Pond, Kings Ridge Pond, North Arm Pond, Dan's Shanty Pond, N. Valley Pond) or by sand (Lake Arthur). Most other sites had very turbid silty water with silt or sandy silt sediment. Only South Lake Sulivan and the upland Adam Tarns have clear water. Perhaps because of the late summer survey period, most of the sites did not have hydrologically active inflows/outflows. Nevertheless, the small and ephemeral appearance of many of these flow channels indicates that run-off is not a major factor in this relatively low rainfall region. The sustained high winds must also contribute to much higher evaporative losses than expected. Most of the ponds and lakes samples seemed to possess fairly stable water levels despite being < 50 cm deep and these sites must be linked with adequate ground water sources. At other shallow sites (e.g. South Sulivan Lake, Kings Ridge Pond, and perhaps Mappa pond, the most brackish site) water level was low and in dry years these probably dry out completely. All the flowing waters were clear, shallow and possessed fast or moderate flow when sampled.

Water quality: Although only conductivity and pH are currently available is was clear from these measurements that acidity and moderate dissolved solid concentrations characterize most of the Falklands water bodies. At some sites, acidity was exceeding low and this can be linked to organic acidity from local peat drainage (e.g. Dan's Shanty Pond, Sand Pass Pond) however, where dissolved humic material is low (e.g. Long Pond), a catchment source of mineral acidity (by calcium sulphate) is suspected. The low base status (particularly of calcium) of Falkland Island soils clearly makes drainage waters pre-disposed to acidification. High turbidity caused by wind-induced sediment resuspension is a natural characteristic of many Falkland Island standing water bodies and none of those sampled was the turbidity attributable to direct human disturbance. Nutrient levels appeared to be low at all sites samples but detailed results are not yet available. Possibly the only exception was Long Pond (near the Mt. Pleasant complex) where domestic waste had been buried, doubtless with consequent leaching of pollutants to the surrounding water.

The flowing waters tend to be less concentrated than in the ponds and lakes but higher than in the upland tarns. All the flowing water appeared to be in good condition and, doubtless, all have high levels of dissolved oxygen and low nutrients. Some local in-wash of silt to drainage systems from disturbed areas (road works etc.) was occasionally noticed but not at the sampled sites.

Aquatic Biology: The freshwater bodies of the Falklands are all characterized by low biological productivity and the survey found no evidence of nutrient enrichment from farming or other activities. Despite low productivity and generally low diversity, the aquatic biota is characterized by some unusual and interesting species. Of particular interest is the relationship with species in acid waters in the UK. Preliminary results from the diatom analysis indicate that many acidophilous diatom taxa on the Falkland Islands are also common in the acid waters of western Scotland. On the other hand, there is another component of the diatom flora that is South American in nature and another (a small number of taxa) that may be previously unrecorded. Zooplankton (like the diatoms) were present in all sites sampled and of particular interest are the large red-pigmented copepods in the tarns and peaty pools. Less pigmented large forms were also characteristic of some of the most turbid sites (e.g. Laguna Babas) and since phytoplankton is very scarce these must likely be feeding carnivorously or on suspended bacteria. The distribution of gammarids and other aquatic invertebrates awaits further taxonomic work but there are clear distributional differences across the Islands but with an overall paucity of species generally, specifically so in the ultra-oliogotrophic tarns and those sites with a pH below ~4.5. Aquatic plants are similarly low in diversity but this survey (especially of the submerged habitats) has revealed several new sites for aquatic macrophytes and one new record. Fish were not specifically studied in this survey but the abundance of zebra trout in Halfway House Arroyo is noteworthy.

Environmental change and historical perspectives: Collection and subsequent analysis of lake sediment cores is a convenient way of reconstructing past environmental change. Hence this offers another way of assessing species introductions and changes by pollution, landscape disturbance or by climate change. This was attempted in several lowland sites on the Falkland Islands and in all cases, subaquatic sediment was unsuitable for coring (sediment was either terrestrial peat or sand). In those sites with silty sediment, this was in all cases underlain at a depth of a few cm by hard sand. Clearly, the shallowness combined with vigorous winds means that most biogenic material does not accumulate permanently in these sites. Sites, where long-term sediment accumulation does occur, are in some coastal inlets and in the deeper upland tarns. During the 2001 survey, several trial sediments cores were collected from Adam Tarn. Diatoms were present in the retrieved cores but longer cores are needed. Follow-up coring of this and similar remote upland sites is the most likely to produce evidence not only about climate change (including erosion episodes) but also about low-level air pollution and past episodes of volcanic activity in southern South America through the volcanic ash record.

Future Implications and future work: Based on the initial observations of the 2001 survey, some implications can already be made together with the identification of potential areas for further work.

• The Falkland Island freshwater water bodies are clearly in a fairly pristine state from a water quality perspective however because these natural waters are sensitive to both enrichment and further acidification. Whilst the smaller ponds are unlikely to be affected, the larger sites and particularly the running waters could be detrimentally impacted by future agricultural improvements. Raising the pH and/or increasing nutrient concentration will undoubtedly raise biological productivity but will also cause changes in aquatic species.
• As far as can be inferred at present, the aquatic biotas in the Falkland Island freshwater bodies are also in fairly pristine condition. Although generally species poor, there are some unusual species present and several sites warrant special status. The Sulivan Lakes are already recognised but the Swan Inlets and Laguna Isla (East Falkland) and Hawk's Nest Pond (West Falkland) have considerable biological interest, not least concerning aquatic plants. The upland tarns are also unique ultra-oligotrophic habitats of note but these are unlikely to be affected by future land use changes. Of the flowing water, the Halfway House stream complex is worthy of special interest.
• Threats to freshwater biodiversity in the Falkland Islands concern the following issues:
  • Changes in land use: these are perceived as likely to be mainly the continuation of long-term trends involving the exploitation of grasslands. Plans to raise the quality of agricultural land through carbonate/nutrient additions could have future consequences for run-off water quality. Local effects of accelerated erosion through overgrazing, grassland fires and road building should however also be considered.
  • Air pollution: contamination from atmospheric sources has and will occur in the Falklands. Global pollutants (137Cs and other radionuclide fallout, persistent organic compounds) have already been recorded in the Falklands and southern South America. But as far as is known levels are very low. Perhaps more importantly, the entire Island region is geologically sensitive to acidification from air pollution (cf. sensitive upland regions in the UK). Compared with the UK sources of atmospheric acidity are very small in the Falklands region and water acidification is not perceived as a problem at present (to be confirmed by sediment core analysis later in this project). If however, fossil fuel usage were to increase markedly in southern South America, the Falklands could well receive a significant deposited acidity.
  • Climate: climate change is a global issue and although the ozone hole now includes the Falkland Islands there is no evidence that freshwater systems are affected on the Islands. However, without regular monitoring of the freshwater ecosystems, initial effects may be unrecognised. Zooplankton in the clear water sites was heavily pigmented (a known response to high UV light levels) but we do not know if this is a recent or persistent condition.
  • Species introductions: the plight of the native trout (Aplochiton zebra) is relatively well known but this is not the case for other aquatic species. This study already indicates that a few diatom species are local (southern South American forms) but many are cosmopolitan and several may be new taxa. Detailed species information on aquatic invertebrates is not yet available but again without historical records recognising recent additions to the biota is difficult. Microfossil analysis of sediments is one way to detect such changes (results from the upland site sediment cores are in preparation).

The initial results of this spatial survey involving a selection of freshwater bodies on the Falkland Islands indicate that all the investigated sites are in nearly pristine condition despite some problems with species introductions and local erosion. However, without historical information (from sediment cores or from monitoring) current trends in aquatic ecosystem change cannot be assessed. The new EU Water Framework Directive for freshwaters stresses the need to undertake both chemical and biological assessment, through monitoring, as part of a wise management strategy for freshwaters. Together with the need to satisfy biodiversity responsibilities, it is recommended that the baseline information being made available by the 2001 survey be used in future evaluation comparisons by repeating the survey every ten years. Some regular annual monitoring of Falkland freshwaters, especially those of interest for fish and birds, should be instigated as soon as is convenient.