This study examines secondary production and periphyton-invertebrate food web energetics at two sites in an industrially contaminated, nutrient-enriched stream. Secondary production data and data from the literature were used to calculate potential amounts of mercury transferred from periphyton to chironomid larvae and into terrestrial food webs with emerging adults. The nutritional quality of periphyton was characterized using energy content, chlorophyll a, protein, ash-free dry mass (AFDM), and percentage of organic matter. Chironomid larvae (Orthocladiinae: Cricotopus spp.) comprised 96% of all macroinvertebrates collected from stones at the two sites. Cricotopus production was extremely high: production was 59.5 g AFDM x m(-2) x yr(-1) at the site upstream of a 1-ha settling basin and 32.4 g AFDM x m(-2) x yr(-1) at the site below the basin. Apparent differences in annual secondary production were associated with reduced organic content (i.e., nutritional quality) of the periphyton matrix under different loading of total suspended solids. The periphyton matrix at both sites was contaminated with inorganic (Hg(II)) and methyl (MeHg) mercury. The amount of Hg(II) potentially ingested by Cricotopus was calculated to be 49 mg Hg(II) x m(-1) x yr(-1) at the upstream site and 19 mg Hg(II)x m(-2) x yr(-1) at the downstream site. Mercury ingestion by Cricotopus at the downstream site was calculated to be 2% of the estimated annual deposition of particulate-bound Hg(II) to the stream bed. Emergence of adult Cricotopus was calculated to remove 563 microg Hg(II)x m(-2) x yr(-1) from the stream at the upstream site and 117 microg Hg(II) x m(-2) x yr(-1) at the downstream site, which amounted to 4.1 g Hg(II)/yr for the 2.1-km reach of stream included in this study. The ratio of metal export in emergence production to surface area for the study stream was 10 to 10(3) times higher than ratios calculated for lakes using data from the literature. This study is the first well-documented example of extremely high aquatic insect production in an industrially contaminated, nutrient-enriched stream, and it highlights the application of production measurements to examine the role of aquatic insect production in the trophic transfer of energy and persistent contaminants in aquatic food webs and into terrestrial food webs.

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We examined the foraging and production ecology of a top predator (Belostoma bakeri, Belostomatidae) in the fishless, thermally constant aquatic ecosystem of Montezuma Well, Arizona. Our results highlight the importance of prey behavior in energy flow in aquatic ecosystems. B. bakeri captured more amphipods (Hyalella montezuma) than damselfly nymphs (Telebasis s&z) in laboratory experiments; H. montezuma spent significantly more time moving than damselfly nymphs did. Also, B. bakeri captured significantly more adult (L 3 mm) amphipods than juveniles (< 3 mm) in the light but not in dark treatments. Production by f. bakeri was 2.8 g dw m-2 yc-' (+2 SE = 0.3). Mean annual standing stock was 0.214 g m-2, annual P: B ratio was 13.3, cohort P: B was 4.7, and annual energy production was 5.88 x lo4 J m-2 yr-I. Ecological efficiency was 13.2% between primary producers and amphipods in Montezuma Well, 5.1% between amphipods and damsclfly nymphs, and 2.7% between lower levels and aquatic heteropterans. Production by B. bakeri made up 25% of the total energy incorporated in secondary consumer production and accounted for 72% of the production by the top predators in Montezuma Well.

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Annual production for the odonate Telebasis salva (7.9 g dry weight [dw] m-2 yr-~, +2 SE = 1.2) was found to be an order of magnitude higher in the thermally constant (21 + 4?C) ecosystem of Montezuma Well, Arizona, than production for multi-species damselfly assemblages in other aquatic ecosystems. Telebasis salva was univoltine in Montezuma Well; larval development took 270.1 d in the laboratory (21?C). Both production (2.1 g dw m-2 yr-1) and mortality (62.2%) were highest for individuals 2-3 mm in body length. Mean annual biomass was 0.78 g dw/m2, annual P/B ratio was 10.0, cohort P/B was 7.5, and annual energy production for T. salva was 1.58 x 105 J m-2 yr-~. Density, standing stock biomass, and production of T. salva were higher in the top 50 cm of the littoral water column than in the 50-100 cm stratum. Densities of a major prey (Hyalella montezuma, Amphipoda) and predator (Belostoma bakeri, Heteroptera) of T. salva nymphs were also estimated. Macroinvertebrate community production, trophic structure, and energy transfer in Montezuma Well are presented. Constant warm water temperature, abundant food, absence of fish, and high predation by invertebrates contribute to the high production rates of T. salva in Montezuma Well.