Riparian forest management substantially affects transport of various materials (e.g. sediment, organic matter, nutrients) through river systems to estuaries [1-6]. These materials have a potential cumulative effect on the physical and chemical structure of habitats and food webs in downstream ecosystems. In the BC coast area, there are many steep mountainous streams, and some of them transport substantial amounts of terrestrial organic materials to their estuaries [7, 8]. However, it is unclear how forestry activities in riparian areas modify downstream ecosystems and how far along streams they affect, because specific indicators and thresholds have not been established to coherently assess effects of forest management on downstream ecosystems. The development of these indicators and thresholds will enhance forest management schemes. To date, although it has been shown that forestry activities in riparian area substantially modify terrestrial material inputs, food webs and biota in its adjacent stream [9-13], fate of fluvial materials exported from such sites and its subsequent effects on downstream ecosystems have not been tracked. The objectives of this project are to (1) analyse longitudinal transports of particulate organic matter (POM) exported from upstream riparian forest management sites, (2) analyse biological effects of the exported POM on downstream ecosystems including estuaries, and (3) propose biogeochemical indicators and thresholds to assess effects of upstream riparian forest management on downstream ecosystems. In this proposal, ?downstream? is defined as the reach below which forestry activity has been operated including the estuary, while ?upstream? includes the forestry activity site. The biogeochemical indicators will be based mainly on quantity and quality of POM in downstream systems as well as at riparian forestry management sites. The threshold will define levels of the indicators above/below which food webs or biota of downstream systems are significantly altered. Our literature review suggests that to develop such tools, two scientific issues need to be overcome: how to track longitudinal transport of upstream-origin POM (UPOM), and what to consider as factors controlling UPOM effects on downstream ecosystems. In other words, without solving them, it cannot be tested whether upstream forestry management affects downstream ecosystems. Stable isotopes (SI) of carbon (C) and nitrogen (N) and some other elements are very commonly used to differentiate ?autochthonous and allochthonous? organic materials in various aquatic systems. SI signatures probably have the most potential as tracers to track UPOM in downstream systems. However, algal production and terrestrial material input to stream systems alter the relative contribution of UPOM to downstream POM [14-17], and potentially complicate detection of UPOM in downstream systems by SI signatures. Thus, it is difficult to determine spatial origins and historical records of downstream POM only by SI signatures. In previous studies of river, d13C of fine POM (FPOM) showed simple increasing trends from upstream to downstream as primary productivity increasing . This suggests that SI of FPOM was dominantly controlled by the balance of fluvially transported FPOM and FPOM from primarily producers, and that budgetary analysis along stream systems could be effective to examine FPOM transport in downstream systems. In a budgetary approach, however, quantifications of various fluxes (e.g. deposition, resuspension, terrestrial POM input, primary production) generally complicate procedures. In stream systems with relatively steep gradient, which dominate the BC southwest coast and are targeted in this project, although FPOM is thought to flow downstream quickly , the relative importance of the processes for FPOM budget is still unknown. Both SI and budgetary approaches have their own advantages, therefore, they will be applied together in this project. A ...
Sakamaki, Takashi, Shum, Jennifer; Richardson, John S.. 2008. Biogeochemical indicator and threshold for assessing ecological impacts of riparian forest management on downstream ecosystems. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2008MR105
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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