Dev K. Niyogi

Effects of Stress from Mine Drainage on Diversity, Biomass, and Function of Primary Producers in Mountain Streams

This paper proposes a hypothesis that relates biodiversity, community biomass, and ecosystem function to a gradient of stress. According to this hypothesis, biodiversity has a low threshold of response to stress, whereas biomass and function are stable or increase under low to moderate stress and decrease only under high stress. This hypothesis was tested by examining communities of primary producers in streams under stress from mine drainage in the Rocky Mountains of Colorado, USA. Mine drainage exerts chemical stress (low pH, dissolved metals) as well as physical stress (deposition of metal oxides) on stream biota. Diversity of primary producers was usually more sensitive to stress from mine drainage than community biomass (chlorophyll a) or primary production. Diversity was negatively related to all stresses from mine drainage, but it was especially low in streams with low pH or high concentration of dissolved zinc. Biomass and production were high in streams with only chemical stress, but they were often low in streams with physical stress caused by metal oxide deposition. Stream sites with aluminum oxide deposition usually had very little algal biomass. The rate of metal oxide deposition, presence of aluminum oxides, and pH together explained 65% of the variation in biomass. The rate of net primary production was highly correlated with biomass and had a similar response to stress from mine drainage. Overall, chemical stresses (low pH, high concentration of zinc) generally led to the hypothesized trends in our model of ecosystems under stress. Physical stress (deposition of metal oxides), however, led to variable responses, and often decreased biomass and function even at low intensity, contrary to the original hypothesis. Thus, the nature of ecosystem response to stress may differ for chemical and physical stresses.

LITTER BREAKDOWN IN MOUNTAIN STREAMS AFFECTED BY MINE DRAINAGE: BIOTIC MEDIATION OF ABIOTIC CONTROLS

Breakdown of plant litter in streams was studied as an example of a major ecological process subject to change through multiple stresses associated with mine drain- age. Rates of litter breakdown were measured at 27 sites in streams of the Rocky Mountains of Colorado, USA. Eight of the sites were pristine, and 19 were affected to varying degrees by mine drainage. The pH, concentrations of dissolved zinc, and deposition rates of metal oxides were measured in each stream. Rates of litter breakdown were estimated from changes in mass of willow leaves in litterbags. Biomass of shredding invertebrates in litterbags was monitored at each site, as was microbial respiration on litter. Of the abiotic variables, increased concentrations of zinc and increased deposition rates of metal oxides were most closely related to decreased rates of litter breakdown. Biomass of shredding invertebrates was negatively related to concentration of dissolved zinc and deposition of metal oxides and was more closely related to breakdown rates than was microbial respi- ration. Microbial respiration was related negatively to deposition rates of metal oxides and positively to nutrient concentrations. Shredder biomass and microbial respiration together accounted for 76% of the variation in breakdown rates. Remediation schemes for streams affected by mine drainage should take into account the distinct ecological effects of the multiple stresses caused by mine drainage (pH, high concentrations of dissolved metals, deposition of metal oxides); remediation of a single stress is likely to be ineffective.

Acute toxicity of ammonia to four species of marine amphipod

Abstract Ammonia has been found to be toxic to many species of marine organisms, but little data address the toxicity of ammonia to benthic infaunal species such as amphipods. Organisms closely associated with marine or estuarine sediments may be exposed to higher ammonia concentrations than are found in the water column, especially when sediments are disturbed. In this study, four species of marine or estuarine amphipods ( Rhepoxynius abronius, Eohaustorius estuarius, Ampelisca abdita and Grandidierella japonica ) were exposed to ammonia in seawater, in the absence of sediment, under controlled laboratory conditions, to determine the concentrations of ammonia that would be acutely toxic to those species. A. abdita was found to be the most sensitive to ammonia, with a median lethal concentration (LC 50 ) of 49·8 mg/liter total ammonia (0·83 mg/liter as un-ionized ammonia). R. abronius was also relatively sensitive: LC 50 = 78·7 mg/liter total ammonia (1·59 mg/liter un-ionized ammonia). E. estuarius and G. japonica were less sensitive, with estimated LC 50 values of 125·5 mg/liter and 148·3 mg/liter total ammonia, respectively (2·49 mg/liter and 3·35 mg/liter un-ionized ammonia). The absence of sediment did not appear to influence the response of the amphipods over the 96-h exposure period.

Biofilm Bacterial Community Structure in Streams Affected by Acid Mine Drainage

ABSTRACT We examined the bacterial communities of epilithic biofilms in 17 streams which represented a gradient ranging from relatively pristine streams to streams highly impacted by acid mine drainage (AMD). A combination of automated ribosomal intergenic spacer analysis with multivariate analysis and ordination provided a sensitive, high-throughput method to monitor the impact of AMD on stream bacterial communities. Significant differences in community structure were detected among neutral to alkaline (pH 6.7 to 8.3), acidic (pH 3.9 to 5.7), and very acidic (pH 2.8 to 3.5) streams. DNA sequence analysis revealed that the acidic streams were generally dominated by bacteria related to the iron-oxidizing genus Gallionella, while the organisms in very acidic streams were less diverse and included a high proportion of acidophilic eukaryotes, including taxa related to the algal genera Navicula and Klebsormidium. Despite the presence of high concentrations of dissolved metals (e.g., Al and Zn) and deposits of iron hydroxide in some of the streams studied, pH was the most important determinant of the observed differences in bacterial community variability. These findings confirm that any restoration activities in such systems must focus on dealing with pH as the first priority.

Land use and stream ecosystem functioning: nutrient uptake in streams that contrast in agricultural development

Rates of nutrient uptake were measured in streams with varying amounts of agricultural development in their catchments. We conducted short-term (1- 3 h) relea- ses of nitrate and phosphate in seven streams in summer and five streams in winter, measuring uptake from downstream changes in nutrient concentrations after correction for dilution. Nitrate (NO3 - ) uptake lengths varied from 45 to 3560 m across sites and seasons, and soluble reactive phosphorus (SRP) uptake lengths from 80 to 1310 m. In streams monitored in both seasons, uptake lengths were generally longer in winter, when discharge was higher and temperatures were lower. Uptake lengths of both nutri- ents were positively related to discharge. NO3 - uptake velocity was related to nitrate concentration and benthic chlorophyll standing stock, which together explained 55 % of its variation. SRP uptake velocity was related to chlorophyll standing stock, and a multiple regression that included SRP concentration and chlorophyll concentration ac- counted for 34 % of the variation in uptake velocity. There was no clear evidence of saturation of nutrient uptake at high background concentrations in the streams. Nutri- ent uptake in these streams was not closely related to estimates of transient storage of water. Catchment land use influenced streamwater concentrations of nutrients and to a lesser extent chlorophyll standing stocks, and these two stream characteristics affected nutrient uptake in these streams.

Headwater stream response to grassland agricultural development in New Zealand

Abstract Agricultural development of native grasslands may change stream physico‐chemistry in ways that provide both subsidies and stresses to the system. The aims of this study were to determine: (1) which physico‐chemical parameters respond most strongly to agricultural development; (2) how biodiversity, community composition, and food‐web structure responded to these changes; and (3) to determine the balance between negative and positive impacts of these subsidies and stresses based on the analysis of 18 headwater streams. Developed pasture streams had increased nutrient loading, alterations to streamside vegetation, increased fine sediment composition, and lower moss coverage of stream‐beds than undeveloped or lightly grazed native grassland catchments (which could not be distinguished from one another). These differences were associated with higher numbers of macroinvertebrate taxa and higher numbers of macroinvertebrates indicating that the net effects of these subsidies and stresses associated with agricultural development were positive within these headwater stream reaches.

Heavy metals: confounding factors in the response of New Zealand freshwater fish assemblages to natural and anthropogenic acidity

Acidification of freshwaters is a global phenomenon, occurring both through natural leaching of organic acids and through human activities from industrial emissions and mining. The West Coast of the South Island, New Zealand, has both naturally acidic and acid mine drainage (AMD) streams enabling us to investigate the response of fish communities to a gradient of acidity in the presence and absence of additional stressors such as elevated concentrations of heavy metals. We surveyed a total of 42 streams ranging from highly acidic (pH 3.1) and high in heavy metals (10 mg L(-)(1) Fe; 38 mg L(-)(1) Al) to circum-neutral (pH 8.1) and low in metals (0.02 mg L(-)(1) Fe; 0.05 mg L(-)(1) Al). Marked differences in pH and metal tolerances were observed among the 15 species that we recorded. Five Galaxias species, Anguilla dieffenbachii and Anguillaaustralis were found in more acidic waters (pH<5), while bluegill bullies (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) were least tolerant of low pH (minimum pH 6.2 and 5.5, respectively). Surprisingly, the strongest physicochemical predictor of fish diversity, density and biomass was dissolved metal concentrations (Fe, Al, Zn, Mn and Ni) rather than pH. No fish were detected in streams with dissolved metal concentrations >2.7 mg L(-)(1) and nine taxa were only found in streams with metal concentrations <1 mg L(-)(1). The importance of heavy metals as critical drivers of fish communities has not been previously reported in New Zealand, although the mechanism of the metal effects warrants further study. Our findings indicate that any remediation of AMD streams which seeks to enable fish recolonisation should aim to improve water quality by raising pH above approximately 4.5 and reducing concentrations of dissolved Al and Fe to <1.0 mg L(-)(1).

Longitudinal changes in biota along four New Zealand streams: Declines and improvements in stream health related to land use

Abstract We studied four streams in southern New Zealand in 2002 to document downstream changes in water quality, habitat, and stream biota in relation to land use. Two streams were in catchments that had increasing intensity of agricultural development downstream from relatively pristine headwaters. A third stream had the most intense land use in the headwaters and a riparian corridor of regenerating native forest along its middle reaches. A fourth stream had low intensity pasturing in its lower reaches, but also downstream increases in sedimentation from natural and historic mining sources. Four to six sites were sampled along each stream. Pastoral land cover in catchments was positively related to nutrient concentrations and fine sediment cover in the streams. At the most agricultural sites, dissolved inorganic nitrogen reached concentrations of 2 mg/litre, and fine sediment covered 33% of the stream bottom. Several biotic indices for invertebrates, including the Macroinvertebrate Community Index (MCI), were lower at the agricultural sites, which had MCI scores around 100. The indices were negatively related to fine sediment cover. The site with the intact riparian zone had declines in sedimentation downstream, which were paralleled by increases in invertebrate richness and biotic indices. Our findings support the notion that the restoration of riparian zones can improve stream habitat and invertebrate health.

Development of a Tool to Facilitate Participation of Maori in the Management of Stream and River Health

A cultural health index (CHI) for streams was developed in a program of collaborative research involving members of Ngai Tahu (an iwi [tribe] within the South Island of New Zealand) and ecologists at Otago University. The aim was to provide a tool for effective participation of Maori in resource management decisions. Five cultural values are of central importance to the nature of the CHI: mauri (spiritual life force), mahinga kai (traditional resource harvesting), kaitiakitanga (guardianship obligation), ki uta ki tai (mountains-to-the-sea holistic philosophy), and wai taonga waters that are treasured). The CHI has three components. Forty-six stream sites in two culturally important river catchments were first classified according to whether there is a traditional association with Maori. The second component assessed the historical and contemporary mahinga kai status of the site, including questions of legal and physical access. The third component was a Cultural Stream Health Measure (CSHM) that encapsulates indicators of catchment, riparian, and instream condition in a manner that is consistent with Maori values. The CSHM was found to be significantly correlated with “western” measures of stream health commonly used in New Zealand (Macroinvertebrate Community Index, Stream Health Monitoring and Assessment Kit), and performed at least as well in encapsulating the relationship between land development and stream health. We describe a multistep process by which other indigenous people can develop a cultural ecosystem health measure, and then use the tool to ensure a substantial role in decision making with the agency in charge.

Direct and indirect effects of mine drainage on bacterial processes in mountain streams

The effects of mine drainage on 2 bacterial processes were examined in Rocky Mountain streams affected by mine drainage. Thymidine incorporation into bacterial DNA was measured as an index of bacterial production, and nitrification was examined because it is sensitive to a variety of stressors. These processes, as well as pH, concentration of dissolved Zn, and deposition rate of metal oxides, all of which are influenced by mine drainage, were measured at 37 sites. The concentrations of inorganic nutrients and dissolved organic carbon (DOC), as well as algal biomass (as chlorophyll a), also were measured at each site. The rate of incorporation of thymidine into DNA was negatively related to deposition of metal oxides and positively related to pH, algal biomass, and concentration of DOC. pH, DOC, and algal biomass together explained 59% of the variation in thymidine incorporation among sites in a multiple regression. Metal oxide deposition probably influenced thymidine incorporation through suppression of algal biomass and through sorption of a fraction of the DOC. The nitrification potential for microbes on gravel substratum removed from streams was estimated as the rate of NO3− production following addition of NH4+. Nitrification was undetectable at pH < 5.3 or Zn > 2 mg/L. Low pH (<6, as a categorical variable), concentration of Zn (which had a negative effect), and algal biomass (which had a positive effect) explained 77% of the variation in nitrification potential. The results suggest that bacterial processes vary in their sensitivity to the stressors from mine drainage, and that they can be disrupted both directly and indirectly. Nitrification was sensitive to direct influences of acid mine drainage, namely acidity and dissolved Zn. Low pH also affected thymidine incorporation. In contrast, acid mine drainage indirectly affected both thymidine incorporation and nitrification potential through its influence on algal biomass, which declined in response to deposition of metal oxides.