An ecological study of a small New Zealand stream with particular reference to the Oligochaeta

The composition, temporal and spatial distribution, and productivity of profundal benthos were investigated in a Colorado Front Range reservoir which impounds water diverted from the Western Slope of the Rocky Mountains. Horsetooth Reservoir, 10.6 km × 1.0 km, consists of three basins with depths greater than 50 m connected by two equalizing channels ca. 30 m deep. Water quality parameters did not vary significantly between sites, but temperature, pH, and dissolved oxygen varied seasonally. The composition and organic content of sediment exhibited a gradient from inlet to outlet which significantly influenced faunal density and distribution patterns. Although 28 genera of macroinvertebrates were collected, the oligochaetes Tubifex tubifex (Müller) and Limnodrilus hoffmeisteri Claparède comprised 97.6% of the total organisms. Chironomids comprised 2.2%. The relative contribution of chironomids to total biomass decreased with increasing depth; the reverse was true for oligochaetes. Mean annual density ranged from 3,827 to 51,901 total organisms/m² for six sampling sites. Mean annual biomass varied from 0.16 to 2.3 g ash-free dry wt/m². Annual turnover ratios ranged from 3.6 to 4.5. Annual production estimates varied from 7.2 to 82.8 kg/ha ash-free dry weight, averaging 39.3 kg/ha or 26.9 kcal/m².     

Effect of algal deposition on acetate and methane concentrations in the profundal sediment of a deep lake (Lake Constance)

Abstract In the profundal sediment ot Lake Constance (143 m depth) the temperature is constant at 4 °C. Despite the constant temperature, CH₄ concentrations changed with season between about 120 μM in winter and about 750 μM in summer, measured down to 30 cm depth. The acetate concentration profiles also varied between seasons. In summer, acetate concentration reached a maximum at about 100 μM in 2 or 4 cm depth. In winter, maximal concentrations of about 5 μM were observed over the entire depth. Input of organic material in late spring may be the reason for the seasonal change of both compounds. To simulate such a sedimentation event, intact sediment cores were covered with suspensions of Porphyridium aerugenium or Synechococcus sp. The addition of the phytoplankton material resulted in a drastic increase of acetate concentrations with a maximum at 2 cm depth, similar to in situ acetate concentrations measured in summer. The same applies for CH₄ for which increased concentrations were observed down to 6 cm depth. H₂ concentrations, on the other hand, showed no distinct increase. Treatment of intact sediment cores with ¹⁴C-labeled Synechococcus cells resulted in the formation of ¹⁴C-acetate, ¹⁴CH₄ and ¹⁴CO₂. Maximum concentrations of ¹⁴CH₄ were found at 4 cm depth, i.e. just above the depth to which ¹⁴C-acetate penetrated. The results show that phytoplankton blooms may cause a seasonal variation of acetate and CH₄ in profundal sediments of deep lakes despite the constant low temperature. They also indicate that acetate is the dominant substrate for methanogenic bacteria in the profundal sediments of Lake Constance.     

Nitrate uptake rate in anoxic profundal sediments from a eutrophic reservoir

There is renewed interest in the use of nitrate to treat the profundal zone of lakes to inhibit anaerobic biogeochemical processes that result in the degradation of bottom water quality (e.g., sediment phosphorus release, mercury methylation). In this study we used experimental sediment–water interface chambers to quantify the rate of sediment nitrate uptake (SNU) in profundal sediments from Lake Perris, a eutrophic raw water reservoir in Southern California. Deoxygenated chamber water was spiked with nitrate, and nitrate concentration was monitored over time under quiescent conditions, followed by mixed conditions with average water velocities of 1 cm/s. Key findings included: (1) SNU decreased with decreasing nitrate concentration, (2) SNU was higher under mixed versus quiescent conditions by nearly 50%, and (3) nitrate uptake as a function of nitrate concentration followed a conventional sediment oxygen demand model in which nitrate uptake was proportional to the square root of nitrate concentration. The probable mechanism for elevated SNU under mixed conditions was an increased diffusional concentration gradient combined with a decrease in the diffusional boundary layer at the sediment–water interface, both of which enhanced the flux of nitrate from overlaying water into sediment. Managers planning to implement lake nitrate addition should account for induced nitrate demand when determining dosing rates. For example, based on our modeling efforts from this data set, SNU in Lake Perris could range by an order of magnitude, from around 12 mg N/m²/d under quiescent, low nitrate conditions (0.1 mg N/l) to around 120 mg N/m²/d under mixed, high nitrate conditions (5 mg N/l). Handling editor: L. Naselli-Flores     

A fate-map for cranial sensory ganglia in the sea lamprey

Cranial neurogenic placodes and the neural crest make essential contributions to key adult characteristics of all vertebrates, including the paired peripheral sense organs and craniofacial skeleton. Neurogenic placode development has been extensively characterized in representative jawed vertebrates (gnathostomes) but not in jawless fishes (agnathans). Here, we use in vivo lineage tracing with DiI, together with neuronal differentiation markers, to establish the first detailed fate-map for placode-derived sensory neurons in a jawless fish, the sea lamprey Petromyzon marinus, and to confirm that neural crest cells in the lamprey contribute to the cranial sensory ganglia. We also show that a pan-Pax3/7 antibody labels ophthalmic trigeminal (opV, profundal) placode-derived but not maxillomandibular trigeminal (mmV) placode-derived neurons, mirroring the expression of gnathostome Pax3 and suggesting that Pax3 (and its single Pax3/7 lamprey ortholog) is a pan-vertebrate marker for opV placode-derived neurons. Unexpectedly, however, our data reveal that mmV neuron precursors are located in two separate domains at neurula stages, with opV neuron precursors sandwiched between them. The different branches of the mmV nerve are not comparable between lampreys and gnatho-stomes, and spatial segregation of mmV neuron precursor territories may be a derived feature of lampreys. Nevertheless, maxillary and mandibular neurons are spatially segregated within gnathostome mmV ganglia, suggesting that a more detailed investigation of gnathostome mmV placode development would be worthwhile. Overall, however, our results highlight the conservation of cranial peripheral sensory nervous system development across vertebrates, yielding insight into ancestral vertebrate traits.