Ecohydrology and Hydrologic Engineering: Regulation of Hydrology-Biota Interactions for Sustainability

In our times the so-called spaceship Earth is facing huge global environmental challenges. The planet becomes dry, freshwater polluted, and both terrestrial and aquatic ecosystems’ biodiversity declines. This happens because of profound modifications to hydrological mesocycles. Acceleration of surface water outflow from the landscape has been increased by drainage, deforestation and expansion of impermeable surfaces. Modification of most of the Earth’s surfaces (agricultural and urbanized areas) resulted in reduction of evapotranspiration by biota and increase of evaporation from abiotic surfaces, causing a decline in water recirculation (e.g., convective rains) and retentiveness at a catchment scale. Moreover, the freshwater ecosystems became overexploited, used as sewage recipients and the landscape-level ecological complexity has been reduced. With such a weakened self-purification potential of the landscape emissions from non-point sources of pollution become the dominating limitation of ecosystem services of flowing water systems, exacerbated by river channelization. Also dams, if constructed without bypasses, modify mineral and organic matter transport and reduce migration of organisms along the river continuum (RC). All of the above mentioned forms of human impacts on freshwater ecosystems and coastal zones are interlinked, and might be amplified to various extents on different continents due to demographic and climatic changes.

In the face of the global demographic, economic, and climatic changes, within the context of the United Nations’ Millennium Development Goals, which defined sustainability as a strategic goal for humanity, a new strategy and measures for achieving this goal is an urgent need. Cases when entire civilizations disappeared because of unsustainable resource use were already noted in the past; however, in the Anthropocene era in which we live now humanity is approaching the carrying capacity of the global ecosystem, threatening destabilization at a global extent. To avoid the cascade of environmental consequences and related social conflicts from local to global scales and to achieve sustainability, an urgent shift in paradigm in the environmental sciences is necessary.

There are two extreme approaches to water and environmental management that still prevail: (1) on one side, hydrologists and hydroengineers are concentrated on providing sufficient water resources for the economy with the technical measures; and (2) on the other, ecologists put their utmost attention to the damage to biodiversity or a potential modification to ecology that the hydrotechnical intervention in focus might cause. Meanwhile, the modification of the landscape and as a consequence the land cover driven hydrological cycle went so far that it is impossible to eliminate the ever intensively occurring threats (water deficits and floods; cf., Ryszkowski and Kedziora 1999) with hydrotechnical measures alone. Luckily, there is a steady evolution of the approach in ecological sciences, leading to the transformation of the structure-oriented thinking by the processes-oriented approach (Zalewski 2013). As a consequence, it was possible to start a dialog with hydrological and hydrology-based sciences, and to formulate a transdisciplinary paradigm, ecohydrology (EH), to deal with water-related problems.

The major message of this paper is to initiate a discussion and joint efforts of ecologists, hydrologists, and hydrological engineers for further integration and transformation into practice the advancements of their respective disciplines for sustainability in water resources management. The paper presents several steps to be made, e.g., (1) change in a paradigm of thinking from structure-oriented to processes-oriented, (2) use of ecohydrological biotechnologies based on “dual regulation” and ecological engineering, and (3) introduction of a new model of education. It proves that hydrotechnical solutions do not need to be destructive for ecosystems and biodiversity. If researchers are able to understand how the basic environmental processes were formed by evolution, it will be possible to use hydroengineering solutions accompanied with biotechnologies to solve water quality and quantity issues, and to develop low-cost conceptually advanced methods and system solutions for integrated water resources management (IWRM).

Sustainable development is a well-established concept. However, there are still disputes on how and what would be the best way to achieve it. One of the conflicting issues is cooperation between environmentalists and engineers. It has deep roots in the system of education, which in turn is based on its foundations in the mechanistic and deterministic philosophies of the seventeenth and eighteenth centuries (Renes Descartes, Izaak Newton, and Julien Offray de La Mettrie), the foundations of the current scientific reasoning and analysis. In these paradigms the universe and all its components are determined by the nature of the laws of physics and thus can be predicted. Such thinking implies still deeper and deeper analysis of the components of the matter, which should at the end lead to an explanation of the nature of the entirety. As a result, researchers tend to concentrate on continuously smaller details of the whole, missing the entire nature of the phenomenon. Researchers create teams of specialists who try to deal with the problem with their specific methods. Engineers, who in fact become real decision makers in environmental management, concentrate on reducing the threat of flooding and droughts, and on obtaining the most energy production possible from a given amount of water. Environmentalists instead aim at conserving particular temporal and spatial landscape structures and ecosystems, or restoring them if degraded. Both fragmented views are doomed to failure because, for example, in case of Europe about 70% of land is drastically modified by man and the hydrological cycle is modified to such an extent that conservation or restoration measures can be effective only in a very limited scope. As a result, the technical solutions are already not sufficient to bear the consequences of the observed land cover degradation, which demonstrate themselves in a more stochastic character of hydrological fluxes and increased loads of minerals, nutrients, and pollutions into waters. Should the solution lie in intensifying those antagonistic measures? The key is integration of hydrological engineering knowledge and experience with the ecohydrological methodology in a more holistic framework. Therefore there needs to be a change of the paradigm from reductionist and sectored thinking to a holistic perception of nature. This would in turn let the society go forward to a transdisciplinary scientific approach to provide a methodological background for harmonization of the society needs with the enhanced ecosystems potential (Zalewski 2002a; Zalewski and Robarts 2003; Zalewski 2005; EcoSummit 2012). The holistic concept of nature is a prerequisite for the development of synergistic system solutions integrating engineering and ecohydrological solutions. However, for these solutions to be efficient it is necessary to define the hierarchy of components the holistic concept is based on. The condition sine qua non is acceptance of the following three assumptions:

An intensive change in the mutual relations between humans and the environment begun with the advent of the industrial era. It was fueled by the conviction of an unlimited potential of nature that can be used for any recognized needs of the humanity (UNESCO 2012; Fig. 1). After the phase of a wild exploitation of the natural resources there came a reflection of the need to protect the nature and later on of its restoration.

However, there are two important aspects of the current relations between humans and the environment. The first is a limited understanding among researchers of the integrity of ecological processes, i.e., circulation of water, nutrients, and energy in ecosystems that are governed by evolution and are also under constant modification by man, and of their change over time. Consequently, human actions based on incomplete information and inadequate understanding of the consequences of the planned actions, with no control form the outside lead to degradation of the environment (Zalewski and Penczak 1981) and loss of their fundamental services. The second aspect is an awareness of the complexity of a catchment that is a template for water resource management, including elaboration of river basin management plans. Primarily, every catchment possesses a specific hierarchy of water cycle drivers related to the unique geomorphology, climate, plant cover, and so on. To various extents these drivers were modified due to social development and population growth combined with a variety of economy driven activities such as deforestation, urbanization, industrialization, and transportation. All of the previously mentioned forms of human interventions into water cycle have changed the catchment’s heat budget, wind speed, and rate of water outflows from the catchments accelerating it. This in turn has increased by orders of magnitude the transfer of mineral and organic matter, nutrients, and pollutants from land to rivers, reservoirs, lakes, and costal zones (Meybeck 2003; Wolanski 2007; Chicharo and Zalewski 2012; Kiedrzyńska et al. 2014). As a consequence researchers encounter that the landscapes across all continents become not only drier but also less fertile due to the loss of nutrients and organic matter from soils.

Therefore, while fundamental ecological cycles such as water and nutrient cycling and energy flow become so deeply modified, there is an urgent need to expand the range of available compensatory measures by those aiming at regulation of the processes controlling the water-biota interplay (Fig. 1).

The other two key interconnected issues that need to be addressed are (1) water cycle, and (2) its linkages with biocenoses. Firstly, the hydrological cycle has to be considered as a primary regulator of ecological potential [bioproductivity and biodiversity, e.g., Wojtal-Frankiewicz and Frankiewicz (2010)]. Secondly, understanding of the role of biocenoses in shaping the water and nutrient cycling is fundamental to reversing the declining potential of the biogeosphere (Tilman 1999; Vorosmarty and Sahagian 2000; Rodrigues-Iturbe 2000). In subsequent paragraphs it will be discussed in more detail.

Water is the primary factor limiting and regulating the ability of ecosystems to accumulate carbon, nitrogen, and phosphorus. When water is available ad libitum, then temperature determines the metabolic rates of microbial communities, plants, and poikilothermic animals. Thus, the assimilation of available nutrients is governed by stoichiometric relationships with limitation effect expressed by Liebig’s law of the minimum. Moreover, biodiversity, a fundamental cumulative indicator of the human well-being and the prospects for sustainable future (Millenium 2005), is driven by water availability that determines plant yield (Visser 1971; Rodriguez-Iturbe 2000; Emaus et al. 2006) and solar radiation, related to biomass increase (Kowalik and Eckersten 1984; Kedziora 1996). Hence, in given geomorphological conditions water and temperature are the major determinants of biodiversity and bioproductivity (Fig. 2). This is because the amount of water in a given temperature range determines the amount of carbon accumulated in an ecosystem (in the form of living and decaying organic matter), while the temperature determines the allocation of carbon between the plant’s biomass and soil organic matter. For example, when moving from boreal zone southward to the tropics with an increasing temperature there is a significant shift in allocation of organic matter, and therefore carbon, from soil into biomass. This is explained by the Van Hoff’s law that relates the acceleration of organic matter decomposition processes to temperature increases. Thus, decomposition of organic matter in the soil can be up to 40 times faster in the tropics than in the boreal zones. High nutrients circulation rate and energy supply create good conditions for diversification of microbial, plant, and animal communities, and persistence of favorable mutations through natural selection and adaptation processes. Thus, researchers can assume that opportunities for diversification of genomes can be more than an order of magnitude more favorable in the tropics (biotic) then in the boreal zone (abiotic ecosystem regulation). What is more, under the harsh conditions of boreal zones, the short growing period for plants provides a very limited flow of energy and nutrients, and in consequence, catastrophic events may randomly eliminate emerging new genomes. Thus boreal and high mountainous ecosystems pose lower potential for regeneration and compensation of human impact. A similar phenomenon is observed in deserts where scarce biodiversity and bioproductivity is driven by low water availability and high temperature leading as a consequence to low carbon accumulation in the soils [abiotic ecosystem regulation, i.e., per Zalewski (2002a, 2010); Fig. 3].

An example of the complexity of the interrelations between hydrology and biota, thus justifying the necessity of its profound understanding, is the abiotic-biotic regulatory concept (ABRC; Zalewski and Naiman 1985; Zalewski et al. 1986; Fig. 3). It was inspired by the river continuum (RC) concept (Vannote et al. 1980), which initiated the process-oriented thinking in river ecology, referring to the observed shift in production/respiration ratio in streams from upstream to downstream (Newbold et al. 1982). The ABRC as a background for ecohydrology was inspired also by a scientific debate of ecologists concerning density-dependent (biotic drivers) and density-independent (abiotic drivers) determination of ecosystems structure and functioning. The ABRC novelty was to underline the hierarchy of abiotic and biotic drivers in shaping the riverine ecosystems; only when abiotic (water) factors become stable and predictable the biotic factors start to manifest themselves. Extrapolating this notion into all types of freshwater ecosystems, researchers can expect analogical adaptation for different abiotic stress factors not only in the rivers, but also in lakes and reservoirs. In the boreal zone, riverine organisms adapt to harsh conditions by fat accumulation to compensate for temperature-limited food assimilation during long winters followed by a period of high energy expenditure due to hydrological stress during the snowmelt period. On the other hand, in hot and dry freshwater ecosystems [e.g., Naiman and Soltz (1981)], high metabolic rates of organisms and consequential high oxygen demands clash with the low water oxygen solubility due to high temperature and low oxygen availability during nights resulting from high respiration rates, thereby compromising the efficiency of Krebs cycle metabolic pathways.

An understanding of the relationships expressed by the model (Figs. 2 and 3) is fundamental to reverse the worldwide observed loss of organic matter in soils (UNEP 2008), as well as siltation and eutrophication in rivers, lakes, reservoirs (Hillbrich-Ilkowska 1993), and coastal zones. Understanding of the previously mentioned processes requires an interdisciplinary knowledge of rudimentary physics, chemistry, plant physiology, biochemistry, geography, ecology, and evolution, and should be applied during hydroengineering realizations. What is more, a broad understanding of the previously mentioned processes to a great extent provides scientific background for the development of ecohydrological biotechnologies adaptable for different geographic regions (discussed in subsequent paragraphs).

As mentioned at the beginning, the reductionist conception of nature followed by the sectorial organization of science led to mechanistic and deterministic perception of the environment, and had their consequences in the rally for maximizing resource use with minimal outlays (Fig. 4). However, it is postulated that to achieve sustainability the society needs to optimize their resource use instead of maximizing it.

The holistic conception of nature and its reflection in the transdisciplinary science needs to employ evolutionary and systematic approach to solving environmental problems. Until the early 1970s the ecology concentrated on structure of nature. Eugene P. Odum (Odum 1971) set fundamentals to break this paradigm by focusing on the functionality of ecosystems and their relation to economy. The further progress in understanding ecological processes in rivers (Heynes 1970; Vannote et al. 1980; Junk et al. 1989), reservoirs (Ward and Stanford 1983, 1995; Petts 1984, 1995) and lakes (Gulati et al. 1990; Hillbricht-Ilkowska et al. 2000) created a background for process-oriented approach in ecology (Wilkinson 2006) and a development of a problem-solving science, ecohydrology (Zalewski et al. 1997; Zalewski 2000, 2013). Hence, a paradigm shift to processes-oriented thinking in entire human activity, especially in the interface between ecologists and hydroengineers is necessary for effective implementation of system solutions in the holistically perceived catchment environment.

Process-oriented thinking in the integrative environmental science has to be driven by physics (e.g., thermodynamics is applied in bioenergetics of plants and some organisms expressed by the Van Hoff law, and heat budget of the landscape is quantified by geophysics). Furthermore, it needs quantification of the processes. For example, if due to deforestation of a landscape temperature increases growth rate of plants and poikilothermic organisms may be positively affected and generate increased yields, only if sufficient, increased amount of water is supplied.

Every strategy for success needs to be based on two elements as follows: (1) elimination of threats, and (2) amplification of opportunities to guarantee reaching its goals. For example, aiming at curbing the ever growing social and economic aspirations, exacerbated by the global demographic growth and overexploitation of resources, a factor four concept of von Weizsäcker et al. (1997) could be a viable alternative. It says that humans are able to double the wealth of humanity while halving the resource use through setting a new direction for technological progress. This can be achieved only when the strategy of economic growth is shifted from competition for resources to competition in their efficient use. On the other hand, the enhancement of ecological potential of the highly modified ecosystems, proposed by ecohydrology, is the only alternative for bringing back the degrading global biodiversity and bioproductivity that affects ecosystem services for society and overall resilience of the landscape to environmental and human-induced stress (environmental stability). Therefore, as a transdisciplinary approach, ecohydrology postulates for harmonizing societal needs with the enhanced ecosystem potential.

The fundamental assumption of EH is that water is the major driver of biogeochemical evolution and thus of biodiversity and bioproductivity. Terrestrial and aquatic organisms, through evolution, have adopted certain life strategies to match with the prevailing water quantity and quality dynamics in the catchment (Zalewski 2000, 2002a; Janauer 2000, 2006; Harper et al. 2008). Therefore, biocenotic processes are shaped by hydrology and vice versa, biocenotic structure and interactions to large extent modify hydrological processes, two-way water-biota interplay called “dual regulation.”

The novelty of EH is that it does not only aim to understand the complexity of water-biota interplay, but also develops a methodology how to use the ecosystem properties and the processes as a management tool, often complementary to other water resources management measures (Zalewski 2002a; Zalewski et al. 2003, 2004). Ecohydrology expands the available management measures (conservation and restoration of ecosystems, aimed basically at maintaining their structure) with those of regulation of ecological processes (Zalewski 2013). The regulation measures should be applied primarily in the anthropogenically highly modified parts of river basins, the so-called novel ecosystems (Hobbs et al. 2006), and involve the processes from molecular to landscape scales. As far as the regulation of processes focuses on both the sides of the water-biota interplay the term dual regulation also applies for these intentional actions (Zalewski 2000, 2006b).

Understanding of the processes needs to be primarily focused on the understanding of the hydrology-biota interplay, and the hierarchy of importance of the abiotic and biotic factors that drive the ecosystems structure and functions from molecular to landscape scales. In accordance with that shift, the catchment and hydrological mesocycles should become the template for quantification of the processes and for the strategic spatial planning and environmental resources management. The use of the catchment template for management of existing resources, e.g., in the framework of IWRM, as well as the water cycle template for precise quantification not only of water budgets, but also nutrients, pollutants, ecosystem performance, and socioeconomic processes, provides background for development of systemic transdisciplinary solutions.

In order to stimulate the use of ecohydrology paradigm and its application to solving the sustainability water related issues the three principles of EH were formulated [see below, per Zalewski (2000, 2006a)]. They are the three steps and the three dimensions of analysis leading to understanding of the underlying ecohydrological processes in a given catchment and application of informed solutions. They also provide a systemic framework for integration into integrated water resources management (IWRM).

Whereas IWRM was defined by Global Water Partnership as “a process which promotes the coordinated development and management of water, land and related resources in order to maximise economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems” (Global Water Partnership Technical Advisory Committee 2000) ecohydrology aims at harmonizing society needs with enhanced ecosystem potential through increasing carrying capacity of ecosystems. Therefore, instead of balancing social and economic needs it opts for harmonizing them with ecosystem potential, and instead of/and apart from protecting pristine ecosystems it calls for regulating processes in the novel ecosystems in order to increase their ecological potential in terms of water resources, biodiversity, ecosystem services, and resilience to global change and anthropogenic stress (termed WBSR, from $w$ for water, $b$ for biodiversity, $s$ for services, and $r$ for resilience). As such ecohydrology is compliant with IWRM concept but gives novel potent tools to achieve sustainability.

The first principle of EH, the hydrological principle implies quantification of hydrological processes at the basin scale and the entire hydrological cycle as a template for quantification of ecological processes. The quantification covers the patterns of hydrological pulses along the river continuum and identification of various forms of human impacts, e.g., point and nonpoint sources of pollution. This principle is based in the assumption of superiority of abiotic factors over biotic interactions (Zalewski and Naiman 1985).

The second, ecological principle implies the need for understanding of the evolutionary-established water-biota interplay, and thus quantification of nutrient flows and energy fluxes dynamics at the water cycle and catchment templates defined in the first step. It also calls for analysis of the spatial distribution of different types of ecosystems, i.e., pristine, degraded, and modified, in order to identify the novel ecosystems that are subject for dual regulation. It is based on the assumption that under intensive global changes it is not enough to protect ecosystems, but the processes should be regulated.

Finally, the ecological engineering principle defines ecosystem properties identified in the framework of the first and the second principles as management tools. These tools are complementary to the already used hydrotechnical solutions and should be used towards enhancement of ecosystem carrying capacity for WBSR. The use of the ecosystem properties is compliant with the rules defined for ecological engineering (Mitsch 1993, 2012; Mitsch and Jorgensen 2003), with the following three assumptions in mind:

Ecohydrological biotechnologies are fundamental to the development of the low-cost and low-energy solutions recognized in the European Commission’s strategic documents under the term green infrastructures.

Due to the complexity of the applied knowledge, the application of geographic information system (GIS) and development of mathematical models for high complexity hypotheses testing and decision support systems should be seen as useful tools to test alternative scenarios and implementation of the EH methodology for sustainable water use, ecosystems, and societies (Fig. 6). Mathematical and GIS-supported modeling are cross verified with field experiments. Such interdisciplinary analysis creates a background for integration of the social and economic processes occurring in the catchment into the problem-solving exercise, which creates a background for transition from multidisciplinary and interdisciplinary to transdisciplinary science.

This paper is a result of brainstorming and discussions on several projects listed in this section. The author expresses his gratitude to Kamila Belka for inspiring questions and discussion, and for precise editing of the final version of the paper. The projects involved in the background of this work are the following: