Basal food resource quality and trophic energy flow across the biofilm-consumer interface: aquatic ecosystem response to environmental stressors

农业是造成加拿大许多流域富营养化的主要因素。因此，对农业的潜在影响进行充分监测，对于淡水资源的知情管理决定至关重要。生物评估是一种提供关于生物体对环境压力的反应的信息的方法，从而能够评价人类活动如何影响生物区系。到目前为止，水生生态系统的生物评估一般是基于组合的分类组成的变化。然而，尽管对生态系统健康提供了可靠的估计，但基于分类学的指数侧重于单个生物群体（如藻类、无脊椎动物），而没有评估整个食物网的影响，对在生态系统规模上发挥作用的压力源的影响的了解有限。因此，需要开发生物监测工具，将社区功能和食物网动态结合起来，以反映整个生态系统的生态属性。 脂肪酸（FAs）对生物体至关重要（例如，能量、生殖、细胞膜）。某些必需脂肪酸从食物来源转移到消费者没有或最小的修改，这是无脊椎动物生长/繁殖和能量转移效率的基础，以更高的营养水平。因此，溪流生物膜中的FA分布代表基础资源质量的代表，即，食物网底层的营养质量。FA剖面在不同条件下发生变化，可以作为生物标志物来评估人为胁迫因素（如富营养化和气候变暖）的影响。然而，需要新的知识来支持在生物监测中使用FA，特别是确认这种生物标志物对农业土地利用与水温升高相结合的富营养化的反应。利用NSERC的发现基金，我将致力于五个短期目标：（1）量化生物膜FA的时空变异性;（2）量化生物膜FA在不同磷条件下的响应以及与藻类分类组成和基于磷的指数值的关系;（3）建立土地利用和生物膜FA之间的关系，以确定变化的阈值;（4）确定生物膜FA的变化阈值。（4）确定农业河流富营养化条件下生物膜FA和初级消费者FA之间的关系;（5）评估富营养化对营养链底部生物膜FA的影响是否因水温升高而加剧。我的NSERC探索计划涉及基于围隔实验和实地研究的基础和应用研究。研究结果将通过更好地了解气候变暖下农业土地利用和富营养化对食物网的影响，提高我们对生物多样性和生态系统功能威胁的理解。

Agriculture is the dominant contributor to eutrophication in many watersheds in Canada. Adequate monitoring of potential impacts from agriculture is thus essential to make informed management decisions for freshwater resources. Biological assessment is an approach that provides information on the response of organisms subjected to environmental pressures, allowing for an evaluation of how anthropogenic activities are affecting the biota. To date, bioassessment of aquatic ecosystems has generally been based on changes in taxonomic composition of assemblages. Yet, despite providing reliable estimates of ecosystem health, taxonomy-based indices are focused on individual organism groups (e.g. algae, invertebrates) without evaluating impacts across the food web, and provide limited insight into the effects of stressors that act at the ecosystem scale. There is thus a need to develop biomonitoring tools that incorporate community function and food web dynamics to reflect ecological attributes of whole ecosystems. Fatty acid (FAs) are vital for organisms (e.g., energy, reproduction, cell membranes). Certain essential FAs are transferred from food sources to consumers with no or minimal modification, which is fundamental for invertebrate growth/reproduction and for energy transfer efficiency to higher trophic levels. FA profiles in stream biofilms thus represent a proxy for basal resource quality, i.e., the nutritional quality at the base of the food web. FA profiles change under various conditions, and could be used as a biomarker to evaluate the effects of anthropogenic stressors such as eutrophication and climate warming. However, new knowledge is needed to support the use of FAs in biomonitoring, in particular to confirm the response of this biomarker to eutrophication from agricultural land use in combination with warmer water temperatures. With this NSERC-Discovery grant, I will address five short-term objectives: (1)Quantify the spatial and temporal variability in biofilm FAs; (2)Quantify the response of biofilm FAs under different phosphorus conditions and the relationship with algal taxonomic composition and diatom-based index values; (3)Establish relationships between land use and biofilm FAs to identify thresholds of change; (4)Determine the relationship between biofilm FAs and primary consumer FAs under eutrophic conditions characteristic of agricultural streams; (5)Assess whether the effects of eutrophication on biofilm FAs at the base of the trophic chain are exacerbated by increased water temperatures. My NSERC-Discovery program involves fundamental and applied research based on mesocosm experiments and field studies. The results will improve our comprehension of threats to biodiversity and ecosystem function by providing a better understanding of how food webs will be impacted by agricultural land use and eutrophication in a warming climate.