Grammatical Trusteeship: Semiotic Anthropocentrism and the Limits of Post-Anthropocentric Law in the Te Awa Tupua Act 2017

Scholarly optimism over the global proliferation of Rights of Nature legislation systematically overlooks how legal grammar functionally grants or withholds these rights. This paper introduces "grammatical trusteeship", a structural semiotic condition where human agents serve as indispensable grammatical mediators of non-human personhood, reinstating anthropocentric ontology syntactically even when legislative intent nominally dismantles it in policy. Grounded in Jane Bennett's Vibrant Matter, this study applies a corpus-driven Systemic Functional Linguistic (SFL) transitivity analysis to 147 clauses from the Te Awa Tupua (Whanganui River Claims Settlement) Act 2017, cataloguing Material, Mental, Relational, and Verbal processes alongside the river's participant roles. Findings reveal Te Awa Tupua is positioned as Goal, Phenomenon, or Carrier in 76.2% of clauses, but as Actor or Senser in only 8.8%. This asymmetry constitutes a textual regime conditioning the river's legal personhood upon continuous human activation, narration, and representation. Exposing the disjuncture between the Act's decolonial ontological ambitions and colonial grammatical architecture, this paper argues that post-anthropocentric law requires a grammatical reorientation in encoding ecological agency, not merely new legislative intent. The study contributes a replicable analytical methodology to Environmental Humanities and intervenes in debates on the performative efficacy of Rights of Nature frameworks.