白洋淀附着藻类的初级生产力及其与水质的关系

附着藻类是湖泊中主要的生产者,尤其是草型湖泊。但与浮游藻类相比,针对附着藻类初级生产的研究还相对较少。采用原位调查与实验模拟相结合的方法测定2014—2015年间白洋淀附植藻类和附泥藻类的现存量和初级生产力,并对附着藻类初级生产与白洋淀水体理化参数的关系进行分析。结果表明,不同采样季节的附植藻类和附泥藻类的叶绿素a分别为34.83—245.22μg/cm~2和26.08—297.40μg/cm~2,无灰干重分别为0.46—5.21g/m~2和0.61—5.81g/m~2。两种附着藻类的生物量都在8月最高,4月和11月最低。空间分布上,南刘庄、府河入口的附着藻类生物量显著高于采蒲台和枣林庄。白洋淀附植藻类和附泥藻类的年均总初级生产分别为494.20mg C m~(-2)d~(-1)和474.45mg C m~(-2)d~(-1),呼吸速率为522.63mg C m~(-2)d~(-1)和508.98mg C m~(-2)d~(-1),净初级生产为-28.44mg C m~(-2)d~(-1)和-34.52mg C m~(-2)d~(-1)。白洋淀附着藻类初级生产力具有明显的时空分布规律,8月最高,6月次之,4月和11月最低,空间分布呈自西向东递减的趋势,在府河入淀口和南刘庄处最高,枣林庄和采蒲台最低。水质较好的区域的净初级生产力为正值,表明这些区域附着藻类以自养型群落为主,水质较差区域的净初级生产力为负值,则该区域以异养型群落为主。运用冗余分析法(RDA)探讨附着藻类与水质因子之间的关系,并采用向前引入法对水质因子进行逐步筛选,Monte Carlo置换检验结果显示,总磷、浮游植物叶绿素a、高锰酸盐指数、氨氮、水温、透明度、溶解氧和氮磷比是影响附着藻类生物量和初级生产的关键水质因子。附着藻类的总初级生产与水体富营养化程度呈正相关关系。     

A portable chamber for measuring algal primary production in streams

This paper describes a portable chamber that measures net primary production of stream periphyton using a ¹⁴C uptake method. The unique feature is that substrates are moved through water at a velocity of 20 cm s ⁻¹ rather than moving water over substrates. The chamber consists of a plexiglass cylinder that is 9 cm in height and 15 cm in diameter. On the top of the cylinder is a DC gearmotor powered by a 12 volt, deep cycle, marine battery. The motor turns a shaft that rotates a 13.3 cm plexiglass plate at a velocity of 20 cm s ⁻¹ . Small tiles (3.2 cm × 3.2 cm × 0.5 cm) that have natural algal assemblages are mounted on the rotating plate. After adding 500 ml of filtered stream water and 185 kBq (5 μCi) NaH¹⁴CO₃ to the chamber, the chambers are placed along a stream margin for 5 h. Measurements of ¹⁴C uptake by algae on the tiles provide estimates of net primary production (NPP). To assess the sensitivity and practicality of the chamber, algal primary production was measured in open and closed canopy sections of Kingsley Creek, Randallsville, New York. In autumn, primary production was higher in the open than closed canopy section and NPP was lower in spring in both sections probably because of scouring of algae due to snowmelt.     

Temporal changes in periphyton standing crop during an unusually dry winter in streams of the Western Cascades,Oregon

The effects of light and discharge on standing crops of periphyton in adjacent shaded and open reaches of first to fourth order streams were examined during winter in three streams of the Western Cascades, Oregon. Standing crops were measured in terms of chlorophylla and periphyton biomass at each site on 8 occasions. Open sites supported higher standing crops of periphyton than shaded sites and increases in standing crop were shown to be related to light input at each site. Biomass increased throughout winter until scouring associated with an unusually late winter freshet reduced periphyton standing crops to their lowest observed levels. It is concluded that periphyton levels are affected by a combination of factors of which light levels, and the periodicity of storm events are of major importance.     

Is Net Ecosystem Production Equal to Ecosystem Carbon Accumulation?

Net ecosystem production (NEP), defined as the difference between gross primary production and total ecosystem respiration, represents the total amount of organic carbon in an ecosystem available for storage, export as organic carbon, or nonbiological oxidation to carbon dioxide through fire or ultraviolet oxidation. In some of the recent literature, especially that on terrestrial ecosystems, NEP has been redefined as the rate of organic carbon accumulation in the system. Here we argue that retaining the original definition maintains the conceptual coherence between NEP and net primary production and that it is congruous with the widely accepted definitions of ecosystem autotrophy and heterotrophy. Careful evaluation of NEP highlights the various potential fates of nonrespired carbon in an ecosystem.     

Alteration of Ecosystem Function by Zebra Mussels in Oneida Lake: Impacts on Submerged Macrophytes

Dreissenid mussels (the zebra mussel Dreissena polymorpha and the quagga mussel D. bugensis) are ecosystem engineers that modify the physical environment by increasing light penetration. Such a change is likely to affect the distribution and diversity of submerged macrophytes. Filter-feeding by these mussels has been associated with increased water clarity in many North American and European lakes. In this study, we report the increase in water clarity of Oneida Lake, New York, USA, for 1975–2002 and argue that the increase was caused by zebra mussel invasion rather than declines in nutrients. Over the study period, although mean total phosphorus decreased significantly, the main increase in water clarity occurred after the zebra mussel invasion in 1991. The average depth receiving 1% surface light increased from 6.7 m to 7.8 m after the invasion of zebra mussels, representing a 23% areal expansion. The maximum depth of macrophyte colonization, as measured by diver and hydroacoustic surveys, increased from 3.0 m before the invasion of zebra mussels to 5.1 m after their establishment. In addition, macrophyte species richness increased, the frequency of occurrence increased for most species, and the composition of the macrophyte community changed from low-light–tolerant species to those tolerating a wide range of light conditions. Comparisons with observations reported in the literature indicate that increased light penetration alone could explain these changes in macrophyte distribution and diversity. Such changes will increase the importance of benthic primary production over pelagic production in the food web, thereby representing an overall alteration of ecosystem function, a process we refer to as “benthification”.     

The relationship of floods, drying, flow and light to primary production and producer biomass in a prairie stream

Factors related to autochthonous production were investigated at several sites along a prairie stream at Konza Prairie Research Natural Area. Primary production, algal biomass, litter input, and ability of floods to move native substrate were measured. Additional experiments were conducted to establish the influence of light and water velocity on primary production rates and recovery of biomass following dry periods. The study period encompassed two extreme (> 50 year calculated return time) floods, thus we were able to analyze the effects of scour on periphyton biomass and productivity. Biomass of sedimentary algae was reduced greatly by flooding and did not reach preflood amounts during the 2 months following the first flood. Rates of primary production associated with sediments recovered to levels above preflood rates within 2 weeks. Biomass of epilithic periphyton was not affected as severely as that of sedimentary algae. Little relationship was observed between water velocity and photosythetic rates. Production reached maximum rates at 25% of full sun light. Epilithic chlorophyll levels recovered within eight days following a dry period, and chl a was an order of magnitude greater on rocks than sediments 51 days after re-wetting. Estimated annual rates of primary production were 2.6 times greater in the prairie than in the forest reaches of the stream. The ratio of annual autochthonous:allochthonous carbon input was 4.81 for prairie and 0.32 for the forest. Periphyton production in prairie streams is resilient with regard to flooding and drought and represents a primary carbon source for the system.     

Reconciling Carbon-cycle Concepts, Terminology, and Methods

Recent projections of climatic change have focused a great deal of scientific and public attention on patterns of carbon (C) cycling as well as its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric carbon dioxide (CO₂). Net ecosystem production (NEP), a central concept in C-cycling research, has been used by scientists to represent two different concepts. We propose that NEP be restricted to just one of its two original definitions—the imbalance between gross primary production (GPP) and ecosystem respiration (ER). We further propose that a new term—net ecosystem carbon balance (NECB)—be applied to the net rate of C accumulation in (or loss from [negative sign]) ecosystems. Net ecosystem carbon balance differs from NEP when C fluxes other than C fixation and respiration occur, or when inorganic C enters or leaves in dissolved form. These fluxes include the leaching loss or lateral transfer of C from the ecosystem; the emission of volatile organic C, methane, and carbon monoxide; and the release of soot and CO₂ from fire. Carbon fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to the measurement of C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we can provide a less ambiguous framework for understanding and communicating recent changes in the global C cycle.     

Stream geomorphology regulates the effects on periphyton of ecosystem engineering and nutrient enrichment by Pacific salmon

1. Pacific salmon (Oncorhynchus spp.) returning to streams deliver substantial quantities of nutrients (nitrogen and phosphorus) that may stimulate primary production. Salmon can also affect the phytobenthos negatively via physical disturbance during nest excavation, a process that may counteract the positive effects of salmon‐derived nutrients on benthic algae. The ability of salmon to disturb benthic habitats may be a function of substratum particle size, and therefore, the geomorphology of streams could determine the net effect of salmon on benthic communities. 2. Based on surveys of 17 streams in southwest Alaska before the salmon run and during peak salmon density, we identified size thresholds for the disturbance of substratum particles by salmon and classified particles as vulnerable (<60 mm B‐axis), invulnerable (>110 mm) or transitional (61–110 mm). At the scale of individual rocks, algal biomass on vulnerable substrata decreased at peak spawning (relative to values before the run) as a power function of salmon density; transitional and invulnerable substrata showed no quantifiable pattern. However, invulnerable substrata in streams with more than 0.11 salmon m^?2 showed net algal accrual, or relatively smaller declines in algal biomass, than vulnerable substrata, indicating that large rocks provide refuge for benthic algae from salmon disturbance. 3. We expected that streams with proportionally larger rocks would respond positively to salmon at the whole‐stream scale, after accounting for the relative abundance of rocks of different sizes within streams. Invulnerable rocks made up only 0–12% of the total substratum particle size distribution in salmon‐bearing streams, however, and algal accrual on invulnerable substrata did not outweigh the strong disturbance effects on the more spatially extensive vulnerable substrata. The change in whole‐stream benthic algal biomass among streams was negatively related to salmon density. 4. Stable isotopes of nitrogen (δ¹⁵N) were used to track nutrients from salmon into benthic biota. Periphyton δ¹⁵N on rocks of all size classes was higher at peak salmon spawning than before the salmon run, indicating the uptake of salmon‐derived nitrogen. Peak δ¹⁵N values were positively related to salmon abundance and followed a two‐isotope mixing relationship. The per cent of N from salmon in periphyton was also related to salmon density and was best explained by a saturating relationship. Spring δ¹⁵N was unrelated to salmon returns in the previous year, suggesting little annual carryover of salmon nutrients.     

The relationship between fish yield and primary production in large European freshwater lakes

The data published on fish yield (Yf) and primary production (PP) in three large European freshwater lakes (Ladoga, Ilmen and Pskovsko-Chudskoe) were analyzed on a long-term basis. The ratios between Yf and PP were found to vary from 0.02% to 0.46%. It was shown that there was an optimal level of PP, above which the efficiency of energy transfer in the pelagic food chain began to decrease. An individual optimum of PP was characteristic of each of the lakes studied. This level was primarily determined by the original trophic status of a given lake as well as by its morphometry and hydrochemistry. The results warn practical ecologists against erroneously predicting commercial harvests from PP.     

On carbon sequestration in desert ecosystems

Recent reports of net ecosysytem production >100 gCm⁻² yr⁻¹ in deserts are incompatible with existing measurements of net primary production and carbon pools in deserts. The comparisions suggest that gas exchange measurements should be used with caution and better validation if they are expected to indicate the magnitude of carbon sink in these ecosysytems.     

Production enhancement by artificial upwelling: a simulation study

A coupled physical–chemical–biological ocean model was applied to study primary production in an idealized 60-km long and 4-km wide fjord. Three different scenarios were simulated: (a) Without fresh water runoff; (b) A river at the head of the fjord adds 100 m³ s^–1 fresh water to the surface layer; (c) The river adds 90 m³ s^–1 fresh water to the surface layer and 10 m³ s^–1 enters the fjord through a pipe at 50 m depth. The average productions in the inner 40 km of the fjord for the three scenarios are 68, 70 and 233 g C m^–2 year^–1 respectively. It is thus shown that there is a considerable potential for increasing the primary production in many fjords and coastal areas by submerging some of the river runoff. Because of the higher silicate content of the deeper water, artificial upwelling tends to stimulate diatom more than flagellate growth. This may be beneficial to mariculture developments. The sensitivity of the simulated primary production to horizontal and vertical resolution, horizontal viscosity, vertical diffusivity and viscosity, discharge depth, wind forcing, sill depth and pulsating the discharge is also studied. A simulation where a large river flux (90 m³ s^–1) was submerged, showed that primary production was significantly enhanced in the outer parts of the fjord as well as along the coastline.