Bioassessment leads to better quality water monitoring in Honduras
A biotic index is being developed to monitor water quality in Cusuco National Park, Honduras. Currently only chemical and physical parameters are considered, which provide only a snapshot of conditions in this vital freshwater resource.
In Honduras growing awareness of deforestation and recognition that natural mountain areas play an essential role in providing drinking water led to the Cloud forest decree in 1987 (Decreto 87-87, 5 de August de 1987) protecting all forests above 1800m elevation.
One such cloud forest is Cusuco National Park (CNP) which supplies potable water for numerous surrounding urban regions, the biggest being Cofradia and San Pedro Sula. Despite its national park status, the watercourses in this area are coming under increasing pressure from inputs of sediment, nutrients and pesticides, mostly resulting from illegal forest clearance and agricultural activities such as coffee production. Sewage from villages is also discharged directly to the rivers predominantly at lower elevations in the buffer zone.
Expensive and limited
Despite the recognised importance of these habitats as a freshwater resource, no biotic index is available for the monitoring of the water quality. Current water quality monitoring schemes in Honduras involve chemical and physical parameters. These methods are relatively expensive and effectively only provide a snapshot of conditions at the time of sampling.
Bioassessment approaches provide a more realistic picture of the water quality, including information on conditions over the previous months. Accordingly, a research project was initiated with Operation Wallacea in 2009 to develop bioassessment protocols and metrics based on aquatic macroinvertebrates for monitoring water quality in Cusuco National Park.
The initial step was to document the natural macroinvertebrate community composition and structure. A survey of the streams in CNP considered to be outside the influence of human activity was performed to establish baseline or reference condition.
Site selection was undertaken, making use of a GIS model developed by Nadine Trahan of Eco Logical Research (Logan, Utah, US) and based on geology and river styles, which allowed us to identify a range of possible geomorphological types in the area.
A total of 25 confirmed species (four new to science) have been identified
A total of 30 sites in seven catchments were successfully sampled for aquatic macroinvertebrates in 2009/10, a relatively large number considering the logistical challenge of reaching some of the locations, which range from an altitude of 550m to 2,050m. Biotic sampling consisted of a standard 2-minute multihabitat kick sampling approach using a 1mm mesh pond net.
Of equal challenge has been the identification of the macroinvertebrates. The aquatic invertebrates of Central America are poorly studied with few identification keys available for the region and many taxa new to science. Despite this, so far 72 families have been identified and to date 106 genera.
In contrast to many temperate streams the aquatic fauna here tends to be dominated by caddisfly larvae (Trichoptera). Stonefly (Plecoptera) and mayflies (Ephemeroptera) have only a low diversity with one and six genera respectively recorded in these rivers. The Odonata (dragonflies and damselflies) have received particular attention, with extensive collections of adults and nymphs. A total of 25 confirmed species (four new to science) have been identified from the adult collections.
Most of what we know about the response of freshwater systems to pollution pressures is derived from temperate regions and it is unknown whether water quality metrics, and in particular biotic indices developed elsewhere, can be applied to tropical areas.
Before embarking on the development of a biotic index specifically for this region we have been testing a range of metrics applied in other parts of the world. The results have been very encouraging. While several performed well, Hilsenhoff Iberian BMWP/ASPT1 , a version of the British BMWP/ASPT system calibrated for Costa Rica, was most promising, assigning almost all of our near pristine sites to high quality status.
We are currently considering what minor modification would be required to improve the performance of this biotic index. Part of this involves evaluating the pollution tolerance of the indicator taxa. The ideal would be to examine their occurrence across a pollution gradient; however, it has not been possible to identify sufficient impacted sites that are within the same typology as those within the park area – most of the potential human impact occurs at lower altitudes.
As an alternative approach a series of field experiments were undertaken in June/July 2011 which involved the creation of artificial stream channels adjacent to the streams. The channels were treated with inputs of nutrients or sediments. We are currently examining the response of the macroinvertebrates to the inputs, which should help us refine the biotic index.