An investigation of carbon pathways in New Zealand streams

An investigation of carbon pathways in New Zealand streams was carried out using a multi-faceted, experimental approach. A series of research projects, presented as individual papers, was conducted with special emphasis on consumer processing. Breakdown of mountain beech (Nothofagus solandri var. cliffortiodes) enclosed in coarse-mesh (3 mm) and fine-mesh (0.2 mm) bags was studied in two physically contrasting streams. Weight losses were most rapid in coarse-mesh bags held in Middle Bush Stream, a relatively stable stream with a large shredder population. The rate of leaf breakdown in coarsemesh bags in Craigieburn Cutting Stream was similar to that In fine-mesh bags buried in both streams. Leaves in bags buried in the beds of both streams lost weight more slowly than their surface counterparts and had slightly lower protein levels and respiration rates. Larvae of the caddisfly, Zelandopsyche ingens, were primarily responsible for the rapid disappearance of beech leaves In Middle Bush Stream. Cage experiments demonstrated that larvae grew and survived equally well in both streams and the absence of Z. ingens from the Craigieburn Cutting Stream benthos was attributed to the inability of the stream to retain coarse particulate organic matter inputs. Retention appears to be the key to shredder distribution and abundance and hence is a major factor controlling litter breakdown. The development, structure and utilisation of stone surface organic layers was investigated at two field sites in dark and natural lighting conditions. In the dark at the forest site an organic layer consisting of slime, fine particles, bacteria and fungi developed and attained maximum biomass (0.08 mg.cm- 2 ) in about two months. In the dark at the spring site where water was low in dissolved and particulate organic matter (DOC level <0.5 g.m- 3 ) no organic layer developed whereas under conditions of natural lighting at both sites, layers were dominated by diatoms and/or filamentous algae. Laboratory experiments demonstrated the importance of dissolved organic matter (DOM) as a prerequisite for layer formation. Uptake by micro-organisms accounted for most of the reduction in levels of dissolved organic carbon (DOC) recorded in recirculating stream channels. Radiotracer experiments ( 14C and 144Ce) showed that several common stream invertebrates could feed on "heterotrophic layers" (assimilation efficiencies 18 to 74%) and suggested that the non-autotrophic components of stone surface organic layers are likely to playa significant role in carbon transfer to the benthos, particularly in small, shaded streams. Utilisation of allochthonous and autochthonous inputs by benthic invertebrates was investigated using stable carbon isotope analysis. The faunas of small, forested streams depended primarily on allochthonous sources of carbon whereas variable utilisation of allochthonous and autochthonous materials was shown by species from a grassland stream. Relatively depleted 13C values obtained for the mayfly Deleatidium taken from forested sites suggest that its larvae assimilate algae selectively. A shift to greater dependence on autochthonous energy sources was shown by invertebrates from small recently clear-cut catchments (1-4 years) in response to canopy removal and flushing of forest-derived organic materials. Although only of a preliminary nature, my results suggest that stable carbon isotope analysis is a useful technique for providing insights into trophic linkages within stream communities. Finally, the influence of physical factors and forest type on the distribution of benthic invertebrate faunas in 43 New Zealand streams was investigated using a systematised survey technique. Several common taxa were numerically dominant at most sites regardless of forest type and both distribution of shredders and faunal diversity were related to stream stability. Implications of these findings for forest-stream management are discussed. In general, New Zealand stream ecosystems are viewed as being strongly dominated by physical factors which determine and limit the framework within. which biological communities can function. Integration of the mass-balance and intra-system approaches to carbon processing is suggested as the logical way to promote understanding of carbon flows to, from and within stream ecosystems

The Impact of Weather Change on Honey Bee Populations and Disease

This review provides an overview of the honey bee (Apis mellifera) which is one of the most important pollinators for agriculture and ecosystems, considered a critical yet fragile contributor to world biodiversity and food security among the countless species facing unprecedented challenges due to uneven climate drivers. Scientists are concerned about the impact of climate change on honey bee habitats. This review study looks at the complicated relationship between climate change and honey bees’ health leading to their genetic and behavioural changes. Further, it also mentions how changes in temperature and weather patterns affect foraging, reproduction and colony survival. This study will focus on the different processes that highlight their susceptibility and emphasise the critical need for comprehensive approaches to mitigate the potential consequences through policy implementation. &nbsp

Age and growth of longfinned eels (Anguilla dieffenbachii) in pastoral and forested streams in the Waikato River basin, and in two hydro-electric lakes in the North Island, New Zealand

Growth rates of New Zealand endemic longfinned eels (Anguilla dieffenbachii) from streams in pasture and indigenous forest, and from two hydroelectric lakes (Lakes Karapiro and Matahina), were estimated by otolith examination. Habitat-specific growth was further investigated with measurement of widths of annual bands in otoliths. Longfinned eels 170-1095 mm in length ranged between 4 and 60 years old (N=252). Eels in pastoral streams grew faster (mean annual length increment ±95% CL = 24 ± 3 mm to 36 ± 7 mm) than eels in streams in indigenous forest (annual length increment 12 ± 2 mm to 15 ± 3 mm). Eels from the hydro-electric lakes had growth rates (annual length increments 19 ± 4 and 19 + 7 mm) similar to eels from pastoral streams. Otoliths of most eels showed annual band widths that indicated growth in several different habitats, corresponding to growth during upstream migration, and limited movement among adult habitats. Estimated age at marketable size (220 g) ranged between 7 and 26 years. The particularly slow growth of longfinned eels in streams in indigenous forest has considerable implications for management. The fast growth rates of eels in hydro-electric lakes provides evidence for the potential of increased eel production by stocking. The probable selective production of female eels in these lakes may be nationally important to allow enhancement of breeding stocks

Leaf litter degradation in highly turbid transitional waters: preliminary results from litter-bag experiments in the Gironde Estuary

The rates of decomposition of oak (Quercus robur) leaves have been examined using litter bags in a very high turbidity macrotidal estuary, the Gironde Estuary (S.W. France). The first experiments show a marked decrease in the decomposition rate of oak leaves at the water-sediment interface (mud-contact: anoxic conditions, reduced physical fragmentation) in comparison to the water column. The results point out the impact of hydrodynamic conditions on leaf litter degradation in such fluvio-estuarine systems. Regarding the aquatic-terrestrial linkage, our observations suggest direct changes in leaf decomposition kinetics and then, a potential delay on the recycling and transport processes of coarse particulate organic matter, especially in a context of modification of the natural water flow, due to global and land use changes

Effects of burial on leaf litter quality, microbial conditioning and palatability to three shredder taxa

1. Heterotrophic microorganisms are crucial for mineralising leaf litter and rendering it more palatable to leaf-shredding invertebrates. A substantial part of leaf litter entering running waters may be buried in the streambed and thus be exposed to the constraining conditions prevailing in the hyporheic zone. The fate of this buried organic matter and particularly the role of microbial conditioning in this habitat remain largely unexplored. 2. The aim of this study was to determine how the location of leaf litter within the streambed (i.e. at the surface or buried), as well as the leaf litter burial history, may affect the leaf-associated aquatic hyphomycete communities and therefore leaf consumption by invertebrate detritivores. We tested the hypotheses that (i) burial of leaf litter would result in lower decomposition rates associated with changes in microbial assemblages compared with leaf litter at the surface and (ii) altered microbial conditioning of buried leaf litter would lead to decreased quality and palatability to their consumers, translating into lower growth rates of detritivores. 3. These hypotheses were tested experimentally in a second-order stream where leaf-associated microbial communities, as well as leaf litter decomposition rates, elemental composition and toughness, were compared across controlled treatments differing by their location within the streambed. We examined the effects of the diverse conditioning treatments on decaying leaf palatability to consumers through feeding trials on three shredder taxa including a freshwater amphipod, of which we also determined the growth rate. 4. Microbial leaf litter decomposition, fungal biomass and sporulation rates were reduced when leaf litter was buried in the hyporheic zone. While the total species richness of fungal assemblages was similar among treatments, the composition of fungal assemblages was affected by leaf litter burial in sediment. 5. Leaf litter burial markedly affected the food quality (especially P content) of leaf material, probably due to the changes in microbial conditioning. Leaf litter palatability to shredders was highest for leaves exposed at the sediment surface and tended to be negatively related to leaf litter toughness and C⁄P ratio. In addition, burial of leaf litter led to lower amphipod growth rates, which were positively correlated with leaf litter P content. 6. These results emphasise the importance of leaf colonisation by aquatic fungi in the hyporheic zone of headwater streams, where fungal conditioning of leaf litter appears particularly critical for nutrient and energy transfer to higher trophic levels

Early stages of leaf decomposition are mediated by aquatic fungi in the hyporheic zone of woodland streams

1. Leaf litter constitutes the major source of organic matter and energy in woodland stream ecosystems. A substantial part of leaf litter entering running waters may be buried in the streambed as a consequence of flooding and sediment movement. While decomposition of leaf litter in surface waters is relatively well understood, its fate when incorporated into river sediments, as well as the involvement of invertebrate and fungal decomposers in such conditions, remain poorly documented. 2. We tested experimentally the hypotheses that the small interstices of the sediment restrict the access of the largest shredders to buried organic matter without compromising that of aquatic hyphomycetes and that fungal decomposers in the hyporheic zone, at least partly, compensate for the role of invertebrate detritivores in the benthic zone. 3. Alder leaves were introduced in a stream either buried in the sediment (hyporheic), buried after 2 weeks of exposure at the sediment surface (benthic-hyporheic), or exposed at the sediment surface for the entire experiment (benthic). Leaf decomposition was markedly faster on the streambed surface than in the two other treatments (2.1- and 2.8-fold faster than in the benthic-hyporheic and hyporheic treatments, respectively). 4. Fungal assemblages were generally less diverse in the hyporheic habitat with a few species tending to be relatively favoured by such conditions. Both fungal biomass and sporulation rates were reduced in the hyporheic treatment, with the leaves subject to the benthic-hyporheic treatment exhibiting an intermediate pattern. The initial 2-week stage in the benthic habitat shaped the fungal assemblages, even for leaves later subjected to the hyporheic conditions. 5. The abundance and biomass of shredders drastically decreased with burial, except for Leuctra spp., which increased and was by far the most common leaf-associated taxon in the hyporheic zone. Leuctra spp. was one of the rare shredder taxa displaying morphological characteristics that increased performance within the limited space of sediment interstices. 6. The carbon budgets indicated that the relative contributions of the two main decomposers, shredders and fungi, varied considerably depending on the location within the streambed. While the shredder biomass represented almost 50% of the initial carbon transformed after 80 days in the benthic treatment, its contribution was <0.3% in the hyporheic one and 2.0% in the combined benthic-hyporheic treatment. In contrast, mycelial and conidial production in the permanently hyporheic environment accounted for 12% of leaf mass loss, i.e. 2–3 times more than in the two other conditions. These results suggest that the role of fungi is particularly important in the hyporheic zone. 7. Our findings indicate that burial within the substratum reduces the litter breakdown rate by limiting the access of both invertebrate and fungal decomposers to leaves. As a consequence, the hyporheic zone may be an important region of organic matter storage in woodland streams and serve as a fungal inoculum reservoir contributing to further dispersal. Through the temporary retention of litter by burial, the hyporheic zone must play a significant role in the carbon metabolism and overall functioning of headwater stream ecosystems

Coarse particulate organic matter in the interstitial zone of three French headwater streams

Headwater woodland streams are primarily heterotrophic: they receive substantial inputs of organic matter from the riparian vegetation, while autochthonous primary production is generally low. A substantial part of leaf litter entering running waters may be buried in the streambed because of flooding and sediment movement. Although the general significance of the hyporheic zone for stream metabolism has been reported early, organic matter storage within the sediment of streams has received less attention, with most studies only quantifying accumulations at the streambed surface and ignoring other stream compartments. In the present study, the amounts of three fractions of coarse particulate organic matter (CPOM; > 16, 4–16 and 1–4 mm) were determined in late autumn and early spring in the interstitial and benthic zones of three head- water streams of the Montagne Noire (South-Western France) differing in their substratum grain size. Our findings demonstrated that the total CPOM content in the interstitial zone can be much (up to one order of magnitude) higher than at the sediment surface. The sandy bottomed stream exhibited a higher amount of CPOM (whatever the size fraction) than the two other streams, suggesting that the sediment particle size may be a major determinant of CPOM storage. Given the large amount of organic matter stored in the interstitial zone, this compartment may play an important role for the carbon turnover and associated trophic dynamics in the stream ecosystem

Interactions between fauna and sediment control the breakdown of plant matter in river sediments

1. A substantial portion of particulate organic matter (POM) is stored in the sediment of rivers and streams. Leaf litter breakdown as an ecosystem process mediated by microorganisms and invertebrates is well documented in surface waters. In contrast, this process and especially the implication for invertebrates in subsurface environments remain poorly studied. 2. In the hyporheic zone, sediment grain size distribution exerts a strong influence on hydrodynamics and habitability for invertebrates. We expected that the influence of shredders on organic matter breakdown in river sediments would be influenced strongly by the physical structure of the interstitial habitat. 3. To test this hypothesis, the influence of gammarids (shredders commonly encountered in the hyporheos) on degradation of buried leaf litter was measured in experimental systems (slow filtration columns). We manipulated the structure of the sedimentary habitat by addition of sand to a gravel-based sediment column to reproduce three conditions of accessible pore volume. Ten gammarids were introduced in columns together with litter bags containing alder leaves at a depth of 8 cm in sediment. Leaves were collected after 28 days to determine leaf mass loss and associated microbial activity (fungal biomass, bacterial abundance and glucosidase, xylosidase and aminopeptidase activities). 4. As predicted, the consumption of buried leaf litter by shredders was strongly influenced by the sediment structure. Effective porosity of 35% and 25% allowed the access to buried leaf litter for gammarids, whereas a lower porosity (12%) did not. As a consequence, leaf litter breakdown rates in columns with 35% and 25% effective porosity were twice as high as in the 12% condition. Microbial activity was poorly stimulated by gammarids, suggesting a low microbial contribution to leaf mass loss and a direct effect of gammarids through feeding activity. 5. Our results show that breakdown of POM in subsurface waters depends on the accessibility of food patches to shredders