Maximizing Beneﬁts to Nature and Society in Techno-Ecological Innovation for Water

: Nature-based solutions (NbS) build upon the proven contribution of well-managed and diverse ecosystems to enhance resilience of human societies. They include alternatives to techno-industrial solutions that aim to enhance social-ecological integration by providing simultaneous beneﬁts to nature (such as biodiversity protection and green/blue space) and society (such as ecosystem services and climate resiliency). Yet, many NbS exhibit aspects of a technological or engineered ecosystem integrated into nature; this techno-ecological coupling has not been widely considered. In this work, our aim is to investigate this coupling through a high-level and cross-disciplinary analysis of NbS for water security (quantity, quality, and/or water-related risk) across the spectrums of naturalness, biota scale, and beneﬁts to nature and society. Within the limitations of our conceptual analysis, we highlight the clear gap between “nature” and “nature-based” for most NbS. We present a preliminary framework for advancing innovation efforts in NbS towards maximizing beneﬁts to both nature and society, and offer examples in biophysical innovation and innovation to maximize techno-ecological synergies (TES).


Introduction
Globally, biodiversity, natural areas, and water security are in dramatic decline due to an unprecedented combination of climate, consumption, and pollution crises. Despite increased recognition of humanity's dependence on the ecosystem services (ES) that the natural world provides, status-quo trajectories suggest the overshoot of several planetary boundaries [1]. Nature-based solutions (NbS) are "living solutions inspired by, continuously supported by and using nature, which are designed to address various societal challenges in a resource-efficient and adaptable manner and to provide simultaneous economic, social, and environmental benefits" [2]. While no panacea, NbS aim to reconcile economic development and ecosystem stewardship, with the potential to reduce consumption of natural capital by substituting accrued 'natural interest' from enhancement of ES [3,4]. NbS for water security (acceptable quantity, quality, and/or water-related risk) are highly relevant for both society and nature: 4 billion people face severe water scarcity [5], 1.32 trillion USD is needed annually for water infrastructure just to maintain business-as-usual [6], and changes in environmental flows and water quality are dramatically impacting terrestrial and aquatic biodiversity [7].
As an emerging concept, the terminology and ideology of NbS, and how they differ from existing approaches, are still under debate [8][9][10][11][12][13][14], although there are general criteria [15], including: (i) simultaneous benefits for society and nature; and (ii) its use as a transdisciplinary umbrella that encompasses existing concepts such as 'ecological engineering' and 'blue-green infrastructure' in engineering, 'natural capital' and 'ecosystem services' in economics, 'ecosystem-based principles' and 'ecological intensification' in agriculture, 'landscape functions' and 'rewilding' in environmental planning, and the family of other nature-based approaches, such as 'ecohydrology', 'ecosystem-based adaptation', 'ecosystem-based mitigation', 'eco-disaster risk reduction', and 'natural climate solutions' [11]. The NbS concept has had significant academic discourse on implementation, barriers, policy, and innovation, often with an emphasis on the urban or rewilding context [3,4,9,11,13,[16][17][18]. On the other hand, science, technology, and innovation 'with and for nature' still remains a minor topic in the NbS literature, despite the acknowledgement of their importance in sustainability transitions [16,[19][20][21]. Recently, a nature-based innovation system (NBIS) was described [16], and differentiated from technological innovation systems (TIS) for several key reasons: (i) NbS can be a product or process phenomenon; (ii) NbS generate dispersed, multifunctional, and mainly public values that are difficult to capture by sectoral organizations and markets; and (iii) NbS involve non-human species and ecosystems that may not be easy or desirable to control.
In this work, our aim is to build on the NBIS concept through a high-level and crossdisciplinary analysis of NbS for one sector, water (quantity, quality, and/or water-related risk). To this effort, our analysis examines naturalness, biota scale, and techno-ecological innovation as part of the broader NBIS. We begin development of operational frameworks for innovation efforts in NbS for water to support maximizing long-term benefits for both nature and society.

Methodology
For this analysis, we chose twenty-seven NbS from diverse fields to bridge disciplinary boundaries, including: restoration ecology, blue-green infrastructure, ecological engineering, and environmental engineering. The NbS were selected to highlight the breadth of techno-ecological innovation across time (from present, to near-term future), and place (from local/niche to globally widespread). NbS included are those that both directly sustain existing or create new ecosystems in nature (e.g., forests, wetlands, coastlines, greenspaces) and address water security challenges for society, specifically: improving quality, improving quantity, and/or reducing water-related risk. Thus, indirect supports of nature (e.g., wastewater resource recovery that could displace land use by bioenergy crops [22,23]) were excluded. To limit scope, we focus our discussion on product-like NbS (e.g., restoration, blue-green infrastructure, ecological engineering), and exclude processlike NbS (e.g., conservation, demand management, governance and finance innovation), recognizing that these are complementary, often with greater imperative, to sustainability transitions [24][25][26][27]. We include NbS involving ecosystems across biota scales, from microbiota (e.g., bacteria, archaea, fungi, phytoplankton, zooplankton, protozoa, etc.), to macrobiota (e.g., plants, insects, bivalves, fish, mammals, etc.). We include large and small-scale NbS across spatial landscapes-not just in the urban context (although we include urban greenspaces a part of nature for the purposes of this analysis). We acknowledge that most NbS discussed here are ecosystems designed for the benefit of humans; purported benefits to nature are often those that are also valued by humans (e.g., biodiversity protection, climate change mitigation, aesthetics) [28]. We draw inspiration from both NBIS [16] and techno-ecological synergy (TES) [29] frameworks in our comparitively simplified methodology and discussion on innovation in NbS for water.

Analysis of Naturalness in NbS for Water
NbS occur with varying degrees of 'naturalness' (closeness to an uninfluenced reference ecosystem), from minimal human influence, to modified environments, to human-built grey landscapes [4,10,11,[30][31][32][33][34]. Defining naturalness for NbS is challenging; it invokes a classic dichotomy between nature and technology [35][36][37][38], and the 'uninfluenced' reference state is itself the subject of debate [39]. Martin et al. (2016) argue that technology is best reserved for the "emergency room" and "techno-fix" options should not be the default approach to protecting nature [37]. Schaubroek (2018) rightly suggests a threshold value of naturalness to qualify as an NbS [10], although no such quantitative threshold value has been developed. Thus, for simplified classification purposes here, we use a gradient of naturalness between 'low', 'medium', and 'high'; qualitative approximations to nature somewhat paralleling Eggermont et al.'s (2015) three types of NbS relating to level of human intervention [40]. While this classification might be considered subjective and oversimplified [31], it is a useful starting point when comparing and contrasting NbS from seemingly disparate fields. For example, the difference in naturalness between wetland restoration and hypolimnetic oxygenation might be apparent, but significant evaluation would be warranted if comparing and ranking naturalness between, hypothetically speaking, green roofs and floating treatment wetlands. Of course, naturalness will clearly depend on how a specific NbS is implemented, e.g., a wastewater-fed wetland that results in anoxic conditions and low biodiversity would certainly be less natural than one that promotes the health of native plants and fish [18]. Certainly, a more quantitative assessment of naturalness is needed to evaluate contributions of techno-ecological innovation to NbS; i.e., contextual evaluation of process impacts on ES and biodiversity such as that seen in TES frameworks [22,29,41,42]. Table 1 summarizes direct benefits to society and nature for the selected NbS for water in order of decreasing naturalness. We iterate that Table 1 is not exhaustive; the NbS selected highlight the diversity across the analyzed spectrums-all variations of wetland restoration, bioretention, and living infrastructure would number hundreds. We select only several articles per NbS to highlight the breadth of transdisciplinary research.
As seen in Table 1, we find that, other than afforestation and restoration, few of the NbS analyzed approximate a natural ecosystem, with most having significant technological/designed attributes. This is not necessarily problematic, all NbS we analyzed are more natural than conventional techno-industrial solutions for water. However, it does highlight the clear gap between "nature" and "nature-based", indicating a major priority for ecological design in NbS for water. It also suggests a need for (i) accepted definitions of NbS including threshold values of naturalness and benefits to nature [10], and (ii) a better understanding of the role of technology in a NBIS, as has been sought for sustainability more broadly [19,20,101]. Within the NbS that fall under the 'engineering' categories, a spectrum of naturalness also exists, ranging from the more natural ecological engineering approaches (e.g., wetland restoration [102,103]), to hybrid blue-green infrastructure (e.g., green roofs and constructed wetlands [104]), to the less natural eco-industrial environmental engineering (e.g., bioremediation, some forms of wastewater resource recovery [105,106]). From a transdisciplinary perspective, we note that this naturalness offers somewhat of a disciplinary correlation. 'Technology' has been defined as the "subset of knowledge that includes the full range of devices, methods, processes, and practices that can be used to fulfill certain human purposes in a specifiable and reproducible way" [19,107]. While not discretely defined, ecological engineering often encourages self-design which is not necessarily specifiable and reproducible, and thus can be considered less technological [10,102,103,108]. Blue-green infrastructure and environmental engineering, on the other hand, certainly have more technological characteristics, often aiming to be specifiable and reproducible, and thus "validated" by researchers and industry. Table 1. NbS for water, benefits to society, nature and co-benefits. In order of decreasing naturalness from green to grey.

Analysis of Biota Scale in NbS for Water
As within nature, we find that NbS involve a wide range of biota scale (Table 2), ranging from microbiota (e.g., denitrification walls, reductive dechlorination in bioremediation, algae ponds), to macrobiota (e.g., plants in bioretention, oysters in living reefs, fish in wetland restoration). However, we find no clear trend between range of biota scale and naturalness. In most cases, a greater range of biota scale typically has a higher degree of naturalness, e.g., highly diverse and interacting micro and macro ecological networks are found in highly natural NbS such as wetland restoration. But this is not always the case-bioremediation, biomanipulation, and sub-surface infiltration can involve engineering habitat specific to microbiota while maintaining a relatively high degree of naturalness. We do observe some relationship between biota scale and implementation timescale. Many of the NbS that span the biota spectrum tend to be longer-term interventions on the order of years to decades (e.g., restoration, afforestation), partly because these typically involve ecosystems with slower-growth species (e.g., trees). However, some NbS spanning the biota spectrum mature far more quickly (<5 years), often those that have economic outputs or are hazard-reducing (e.g., agroecology, living infrastructure, riparian planting). Likewise, NbS utilizing microbiota are often far more rapid interventions on the order of weeks to months (e.g., subsurface ecological sanitation, denitrification walls) due to their inherently shorter lifecycles. Again, this is not always the case-e.g., aquifer bioremediation can take years to be successful. We also note discontinuities across many fields involving ecosystem engineering at different biota scales. Ecological engineering, ecohydrology, and blue/green infrastructure tend to focus on diversity and abundance of macrobiota, perhaps due to higher visibility and ease of monitoring; e.g., freshwater invertebrates are often prioritized over the underlying microbial ecology. On the other hand, environmental engineering is often associated with controlled microbiomes [109,110], rarely scaling up to higher trophic biosystems. This is despite a clear interdependence between biota scales, and calls for a more unified ecology [111,112].

Analysis of Benefits to Nature and Society through Techno-Ecological Synergies throughout the Development and Diffusion of NbS
Technological innovation has been defined as the "process by which technology is conceived, developed, codified, and deployed", as one part of a broader innovation system [19,101,107]; i.e., innovation does not occur in a vacuum. Here, we consider technological innovation that enables connections between technological and ecological systems. We recognize considerable work has developed this concept in the TES approach [29], although, for the purposes of our simplified analysis, we distinguish two types of innovation processes: (i) innovation to biophysically integrate natural and ecological systems, and (ii) innovation to maximize ES synergies. These clearly have significant overlap, and both can be thought to operationally advance "availability of technologies supporting NbS development" [16].

Biophysical Innovation
Biophysical innovation is specific to mechanisms that couple the metabolic and information flows between ecological and technological systems. Self-design is a primary example of biophysically linking technological and ecological systems, in which an ecological system adapts to the environmental constraints of the technological system it finds itself in, with minimal human interference [102]. Constructed wetlands that are built to evolve and adapt to fluctuations in runoff quantity and quality are an example of this. Innovation processes that encourage self-design thus lead to higher naturalness (green vertical arrow in Figure  1A). Another biophysical innovation approach, albeit far less natural, is ecological forcing by a technological system. Ecological enrichment is an example of this approach, e.g., forcing a desired microbiome community structure through human activity (e.g., aquifer bioremediation, hypolimnetic oxygenation). This has the opposite effect of self-design, constraining evolution and adaptation of the ecological system, resulting in decreased naturalness (grey arrow in Figure 1) and obligate reliance on human intervention. Less natural solutions, such as ecological forcing, are often justified with techno-economic efficacy rationale. This is despite the fact that many highly natural NbS are lower cost than industrial counterparts over long time horizons [24,32]. New York City's provisioning of drinking water is an oft-cited example, where conservation of watershed lands was far lower cost than installing improved technology. Reliability concerns are another common driver of ecological forcing and/or lower naturalness, e.g., mangrove restoration has shown mixed success in different locations [44], and some NbS for stormwater management have shown up to 6 orders of magnitude of variation in the efficacy of reducing coliforms [113]. NbS that do not reliably achieve societal objectives incentivize actors to revert to readily available industrial technology or stimulate demand for less-natural industrial innovation. Root causes of unreliability include "pervasive knowledge gaps" [24], and variation in local social-ecological systems that suggest challenges for the scalability of "proven" NbS [32,114]. Driving adoption of more natural NbS (horizontal green arrow in Figure 1A) relies on advancing reliability in place and time; e.g., UN Water indicates a need to "test NbS in different hydrological, environmental, socio-economic and management conditions" [32]. Innovation processes that increase naturalness and reliability prior to widespread adoption are thus critical to maximizing long-term benefits.
Yet, this does present a paradox-how can biophysical innovation both increase naturalness (i.e., less controlled and specifiable), and also increase efficacy and reliability (typically more controlled and specifiable)? Technological innovation systems have historically trajected towards advancing efficiency metrics (output divided by input energy/resources), usually accompanied by decreased naturalness. For example, wastewater-fed wetlands were mostly displaced by technologically "efficient" activated sludge tanks-less natural, but more reliable effluent water quality. Moving in the opposite direction presents significant challenges-naturalness is not typically seen as something that can be increased by human activity; rather, it needs be included in ecological design objectives. A major challenge to this is that more natural NbS are more complex systems-decomposing the larger system does not necessarily elucidate its understanding [115]. One plausible workaround to increasing naturalness in NbS is to supplement specific objectives with broader ones, promoting environment-guided function [115]. A rainforest is certainly not a technology, yet effectively and reliably produces food, water, oxygen, and biodiversity. Techno-ecological innovation could better invoke nature by including broad non-specifiable objectives [116] along with one or several specifiable objectives. Agroforestry is a foodsystem example of this biophysical innovation, coupling unspecifiable biodiversity in tree canopies (facilitating naturalness) with crop production (e.g., coffee) in the understory with high efficacy and reliability, and still maintaining some degree of naturalness. For water, Shijun (1985) describes a millennia-old innovation for utilizing wastewater and forest debris in an aquaculture-sericulture pond-forest biosystem [108,117]. The complete system mimics nature and produces non-specific trophic interactions, water treatment, oxygen, and biodiversity, while concurrently achieving several specifiable objectives (fish, silk) within a (relatively) natural biosystem. Technological efficiency is low as it is certainly more efficient to keep silkworms in a single-trophic captivity system; this is because natural systems do not necessarily organize themselves according to efficiency [118]. On the other hand, efficacy and reliability are high; the system continuously produces fish and silk with few non-renewable inputs and maintains itself due to engineered resiliency. Todd et al. (2003) give contemporary examples of utilizing multitrophic engineered ecologies for both broad (biodiversity, carbon fixation, aesthetics) and specific (wastewater treatment, food) objectives [119]. Biophysical innovation for broad and/or multiple objectives also allows for a more adaptive NbS that works with the complexity of nature, and is less likely to experience "catastrophic failure" [120].

Innovation to Maximize ES Synergies
Maximizing ES synergies between technological and ecological systems is the core concept of the TES framework [29], and innovation in NbS can aspire to maximize this synergy. As one (highly simplified) example in the water sector, innovation in technological systems for green roofs can augment synergistic ES in ecological systems. For example, well designed green roof systems will improve water storage, habitat, and nutrient cycling that support the ecological system-plants, microbes, soil animals, urban fauna. By augmenting the ecological system, reciprocal synergistic ES result, e.g., increased transpiration of urban runoff, biotransformation of xenobiotics, strong root systems to prevent soil loss, etc. Design for co-benefits may also result in a solution with increased ES synergies for both nature and society. For example, a single objective of flood control might utilize dams or levees, but adding an additional design objective to also reduce nutrient loading might lead to distributed denitrifying bioswales with greater naturalness and less technological aspects ( Table 2) and cascading co-benefits (i.e., aesthetics, interconnected greenspaces). On the other hand, introducing multifunctionality has the potential to increase complexity, introduce unintended consequences such as positive feedback loops, or deliver sub-optimal benefits [121], e.g., both a poorly functioning wetland and a poorly functioning wastewater treatment system can result from inadequate ecological design [119]. Figure 1B shows high-level categorizations of benefits to nature and society, again acknowledging limitations of the qualitative and subjective conceptualization of "benefits" and "naturalness". Quantitative valuation of ES to society is an ongoing (and contentious) discussion with major consequences for NbS development and diffusion [11]. Likewise, quantitative evaluation of benefits to nature (e.g., restoration, enhancement) requires a broader suite of metrics under current development, such as trophic relationships, gene flows, meta-community interactions [122], and net-positive outcomes [123]. Despite examples that offer tangible benefits to human society and suggest at least some benefit to nature (at least compared to techno-industrial solutions), there has been no longitudinal analysis of quantifying benefits to nature from these types of initiatives, perhaps due to the same incongruencies that challenge ES valuation.

Conclusions
From this work, several key findings emerge:

Conclusions
From this work, several key findings emerge:

1.
NbS for water exist across a wide spectrum of naturalness and biome scale, all generally showing some technological characteristics. While not inherently problematic, we further highlight the significant gap between "nature" and "nature-based", demonstrating the major challenge for both ecological design and innovation systems in NbS that needs to be addressed for comparative analysis and future policy. We find evidence of innovation mechanisms in NbS with potential to increase naturalness. These include, amongst others, biophysical innovation and innovation to maximize ES synergies, and specific examples include design for broad objectives to supplement specific ones, and design for co-objectives.

2.
While increasing naturalness in innovation stages prior to widespread adoption has potential to maximize longer-term benefits to nature and society, this coupling of technological and ecological systems does not come without the possibility of unintended consequences, such as positive feedback loops creating uncontrollable novel ecosystems. "The road to extinction is paved with good intentions" resonates.
To mitigate this risk, robust evaluation methodologies for these coupled systems are urgently needed.

3.
We find examples of innovations, such as the forest-pond biosystem described, that have been ongoing for millennia and purposefully provide benefits to both society and nature. Many Indigenous societies, and even some Western ideals such as permaculture, have a belief system that supports natural systems while achieving societal objectives. Indeed, the Brundtland Report remarked over thirty years ago that the only people with a proven record to achieve sustainability within their ecological limits are Indigenous societies. Despite historical and ongoing environmental and economic injustices, many of these knowledge systems continue and are as relevant today as ever. Innovation policies should acknowledge, learn from, and respectfully invoke at large-scale these "ecological civilization" philosophies before planetary boundaries are further compromised.