The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite abundance; with greater host diversity, parasite levels per host are predicted to be lower due to a higher probability of dispersing parasites encountering non-competent hosts. Dilution effects could also occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competency. The introduction of non-native hosts can change community competency of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish occurring in the presence and absence of non-native Faxonius crayfish in the New River, USA. We performed an experiment investigating the effect of host density (1 vs 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced F. cristavarius is a non-competent host for these worms. Six C. ingens were stocked on a C. chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment . There was no significant effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.
In our writing, we voice stories of two Australian rivers to convey Indigenous ways of knowing and being. Interweaving academic literature, nature writing and creativity, we craft a story of reconnection that is transformative, action-oriented and potentially political. An open mind, place-intuition and the process of attending can deepen our river relationships, creating a sense of love and communicative connectedness. Paying deep attention, we notice meanings embedded in plain sight, within hearing range of rivers and watery places. Our relationships may be ‘in our faces’ such as the wind, or the air, water or bushes nearby. We communicate across binaries to experience the dissolution of imagined barriers. Feeling, hearing, writing and storytelling can support verbalising of experience, helping to bring to mind place-wisdom. It offers an everyday possibility for people now estranged from their riverine kin. The process uses a post human-centred, common worlds frame to consider the Anthropocene in regenerative ways. It is creative and liberating, and rivers are dying for people to take action by speaking out for and with our greater selves. In this learning journey, we synthesise learnings, hoping to inspire people everywhere to hear the call of rivers, to respond, take action and learn to love their rivers again.
In this paper a collaborative writing group explores how we, two rivers, express ourselves over time, place and space, our energies long interpreted as veins and arteries carrying the Country’s life affirming blood. Voiced as River: I, River, this position reflects a worldview in which interrelationship with living river is normal, and River Spirit is ever-present. It is a position underpinned by Indigenous narratives as riverine expressions of place-based love. At times the paper is also voiced as writing group or individuals, with voices being interchanged where required for smooth reading. We see this as part of the decolonising process, which feels liberating and healing amongst the writers. Each writer is equally valued as co-creator, contributor, narrator and story teller. The two Rivers, being Martuwarra Fitzroy River (Kimberley, Western Australia), and Unamen Shipu Romaine River (North Shore, Québec, Canada) illustrate a common condition of being, through heritage, life, change and possibility. Through stories and voices, the socio-scientific implications of colonisation and lost connections become clear, considering the interaction, the dialogue and the cultural synthesis of living water systems that have always incorporated all life forms into rivers of life. As a way of navigating towards wholeness, Aboriginal knowledge systems and narratives for healing are used to bring together findings of this intercultural river learning journey.
Biological invasions are regarded as one of the largest threats to native biodiversity. The eradication of non-native parasites by culling of hosts are a controversial conservation strategy, particularly when using indiscriminate methods involving whole ecosystem collateral damage. While short-term effects are abundantly documented, long-term surveys are needed to detect potential wider ecosystem effects. Here, we report a six-year study on effects of the piscicide rotenone on invertebrate communities from a Norwegian water course using a Before-After-Control-Impact design. Kick-net samples of benthic invertebrates were collected from three lentic sampling stations and two lotic stations two to four times per year in both a control and a treated watershed. In general, only relatively minor short-term effects immediately after the treatment on species turnover, measured as temporal beta-diversity, of benthic invertebrates were observed both in lentic and lotic locations. However, the lotic fauna was temporarily severely negatively affected following a period of rotenone exposure from an upstream lake. Species turnover co-varied markedly between control and treatment locations, indicating that natural environmental variation override effects of rotenone treatment. Likewise, the abundance of invertebrate taxa varied considerably both over time and between control and treatment locations. Our study indicates minor short-term (i.e. < one month) or long-term (i.e. four years) effects of rotenone treatment on benthic invertebrates, but severe effects on the lotic fauna eight months after treatment. However, long-term effects are likely to be taxa-specific and vary depending on habitat connectivity and thus potential for re-colonization and will differ among locations and among taxa.
This study provides a comprehensive review of the existing river measurement data of South Korea. The specific sediment yield in the country is 5–1,500 tons/km 2·year. The watershed area decisively affects the shapes of the curves for flow duration, sediment rating, and cumulative distribution of water and sediment discharge, and it can determine the effects of topographic and anthropogenic characteristics on erosion and sedimentation processes. Regarding flow regime, small watersheds have flashy hydrographs and high sediment concentrations at a given flow discharge. The coefficient of the sediment rating curves for various rivers decreases from 1 to 0.02 as the watershed area increases from 100 to 20,000 km 2, with the exponent of the curves ranging from 1.5 to 2.0. Moreover, sediment transport in small watersheds depends on large floods. The half-yield discharge typically ranges from 5 to 40 times the mean discharge, and it decreases with increasing watershed area. This study proposes equations to calculate the annual discharges, flow duration curves, sediment yield, and cumulative distribution curves of the flow and sediment, as well as the sediment yield at reservoirs in South Korea. Additionally, the sediment regimes in the country are compared to those in other continental regions.