Tolerance values of benthic macroinvertebrates for stream biomonitoring: assessment of assumptions underlying scoring systems worldwide.

Tolerance values (TVs) based on benthic macroinvertebrates are one of the most widely used tools for monitoring the biological impacts of water pollution, particularly in streams and rivers. We compiled TVs of benthic macroinvertebrates from 29 regions around the world to test 11 basic assumptions about pollution tolerance, that: (1) Arthropoda are < tolerant than non-Arthropoda; (2) Insecta < non-Insecta; (3) non-Oligochaeta < Oligochaeta; (4) other macroinvertebrates < Oligochaeta + Chironomidae; (5) other macroinvertebrate taxa < Isopoda + Gastropoda + Hirudinea; (6) Ephemeroptera + Plecoptera + Trichoptera (EPT) < Odonata + Coleoptera + Heteroptera (OCH); (7) EPT < non-EPT insects; (8) Diptera < Insecta; (9) Bivalvia < Gastropoda; (10) Baetidae < other Ephemeroptera; and (11) Hydropsychidae < other Trichoptera. We found that the first eight of these 11 assumptions were supported despite regional variability. In addition, we examined the effect of Best Professional Judgment (BPJ) and non-independence of TVs among countries by performing all analyses using subsets of the original dataset. These subsets included a group based on those systems using TVs that were derived from techniques other than BPJ, and groups based on methods used for TV assignment. The results obtained from these subsets and the entire dataset are similar. We also made seven a priori hypotheses about the regional similarity of TVs based on geography. Only one of these was supported. Development of TVs and the reporting of how they are assigned need to be more rigorous and be better described.

Economic and ecological costs and benefits of streamflow augmentation using recycled water in a California coastal stream.

Streamflow augmentation has the potential to become an important application of recycled water in water scarce areas. We assessed the economic and ecological merits of a recycled water project that opted for an inland release of tertiary-treated recycled water in a small stream and wetland compared to an ocean outfall discharge. Costs for the status-quo scenario of discharging secondary-treated effluent to the ocean were compared to those of the implemented scenario of inland streamflow augmentation using recycled water. The benefits of the inland-discharge scenario were greater than the increase in associated costs by US$1.8M, with recreational value and scenic amenity generating the greatest value. We also compared physical habitat quality, water quality, and benthic macroinvertebrate community upstream and downstream of the recycled water discharge to estimate the effect of streamflow augmentation on the ecosystem. The physical-habitat quality was higher downstream of the discharge, although streamflow came in unnatural diurnal pulses. Water quality remained relatively unchanged with respect to dissolved oxygen, pH, and ammonia-nitrogen, although temperatures were elevated. Benthic macroinvertebrates were present in higher abundances, although the diversity was relatively low. A federally listed species, the California red-legged frog (Rana draytonii), was present. Our results may support decision-making for wastewater treatment alternatives and recycled water applications in Mediterranean climates.