Water Protection Zones—Impacts on Weed Vegetation of Arable Soil

Abstract

The aim of this study is to evaluate the occurrence of weeds under conditions of limited herbicide use due to the protection zone of water resources. A total of 23 weed species were found in maize stands, 19 species were found in wheat stands, and 16 species were found in rapeseed stands. The redundancy analysis (RDA) results show significant differences in weed occurrence and composition due to herbicide regulation in each crop. Changes in weed composition induced by herbicide application limitations lead to a preference for more specialized weed species (specialists) at the expense of widespread species (generalists). Limiting the use of pesticides in sensitive and vulnerable areas, such as water sources, bodies, and watercourses, is justified from the perspective of protecting the aquatic environment and biodiversity. However, such measures can cause weed growth that is difficult to control, and therefore, it is important to search for new methods for weed control in field crops. Determining a balance between safeguarding water resources and addressing agricultural challenges remains crucial for sustainable land and water management.

1. Introduction

Human activity is often the primary source of pollution, bringing potentially hazardous substances into atmospheric, terrestrial, and aquatic ecosystems [1]. Agriculture is one of the largest sources of emissions in surface water and aquatic ecosystems [2,3]. Hoever, aquatic ecosystems are often contaminated with herbicides [4]. This contamination depends on many parameters, such as watershed structure and land use (anthropic activity, surface, and slope), soil structure and composition, environmental factors, hydrology (rainfall, flow, and wind), aquatic environmental conditions (pH, organic matter, and suspended particles), and the chemical properties of herbicides [5,6]. Many European studies have reported the detection of active herbicides such as diuron, metolachlor, isoproturon, terbutryn, and atrazine in aquatic environments [7,8]. Owing to their phytotoxic effects, their behavior in freshwater ecosystems poses a risk to non-target organisms, such as benthic diatoms (Diatomeae) [9]. Herbicides generally inhibit various vital functions in photosynthetic organisms [10]. Weeds have been suppressed since the beginning of agriculture because they are the main biotic cause of yield losses in field crops [11]. A revolution in weed control started in the early 1950s, owing to the use of herbicides, which laid the foundation for industrial agriculture [12,13]. In recent years, increased use of herbicides has been reported in various countries [14,15,16]. During the 12 years of the monitoring of pilot farms in Switzerland, an increase from 0.034 kg/ha to 0.141 kg/ha in glyphosate use in arable land was recorded [17].

The use of pesticides is one of the most debated aspects of agricultural intensification, given their potential direct and indirect consequences at the individual, population, and ecosystem levels [18,19]. The direct toxic effects of pesticides can appear quickly after their application [20], whereas the indirect effects of pesticides can occur one or several years later [21,22]. The toxicity of pesticides can vary substantially among affected organisms [23,24], and the ecological impacts of pesticides can persist several years after their application [25]. Herbicide use can also reduce shelter for bees, insects, reptiles, etc., in agricultural landscapes [26,27,28].

The leakage of herbicides, or the concept of herbicide loss, is based on spatial heterogeneity, where hydrological factors of the environment dominate, for example, the nature of the first rain event after herbicide application. Several studies have demonstrated that factors such as topography and soil hydrological properties can clarify the spatial patterns of herbicide loss [29]. Some herbicides can be transported from agricultural land to the surface and groundwater, where they can affect the ecosystem [30,31,32].

Pesticides, together with nitrates, currently form the main pollution sources of drinking water in Europe [33]. To limit or at least mitigate the negative effects of agricultural emissions on water, in recent decades, the European Union (EU) has developed an extensive and interconnected regulatory political framework that influences water management, agricultural practices, and environmental protection [34]. For example, the Nitrates Directive (91/676/EEC) [35] builds on the objectives of the Drinking Water Directive (98/83/EC) [36] and the Water Framework Directive (2000/60/EC) [37] to form an overarching framework for EU directives on the specific functions of water, the use of chemicals, and their effect on environmental protection and the state of European waters. Apart from international treaties and EU law, the basic legal regulation in the Czech Republic (CR) governing water protection is Act No. 254/2001 Sb. [38] (water law). Although the directives are linked, their implementation has side effects that prevent the effective protection of drinking water sources. For example, fertilizer use rules are not always beneficial to groundwater and drinking water quality [34]. The adopted EU framework directives reflect a growing awareness of the complexity of the water and river basin issue [39,40,41]. The new provisions related to the Water Directive require interdisciplinary cooperation within individual EU member states and international cooperation [34]. The pesticide regulatory framework in Europe creates strong incentives for growers to reduce herbicide application. In Denmark, since the late 1980s, the demand for herbicides has been increasing; therefore, several pesticide action plans have been initiated [42].

In CR water protection, the use of water and the right to access it are regulated by the Water Act [38]. The Water Act is specified or elaborated upon by subsequent regulations (government regulations and decrees) issued by the Ministry of the Environment together with the Ministry of Agriculture. Subsequent regulations have defined zones of hygienic protection for surface water sources, including rules and restrictions for the use of pesticides.

It should be emphasized that the pollution of aquatic ecosystems by herbicides and pesticides has far-reaching consequences for biodiversity, ecosystem services, and human health [43,44,45]. Pesticides can also negatively affect the environment in ponds, rivers, and other freshwater and marine habitats [46,47].

Restrictions on the application of herbicides in areas of surface water protection have led to a limited choice of herbicides. Different weed regulations create diverse selection pressures on weed vegetation. The aims of this study are (i) to assess the effect of herbicide limitations on the species composition of weeds in selected crops, (ii) to determine the weed species that meet the conditions of limited weed regulation, and (iii) to determine the proportions of neophytes and species with invasive status. Water surface protection based on herbicide use reduction can lead to challenges in the regulation of certain weed species. Increased weed infestation by specific types of weeds without effective regulation can exacerbate conflict between farmers and water management authorities.

2. Materials and Methods

2.1. Study Area

Selected plots are in the cadastral territory of Zarazice (South Moravian Region, Czech Republic). The monitored agricultural holding operates over an area of 200 ha and includes flint maize (Zea mays), winter wheat (Triticum aestivum), winter rapeseed (Brassica napus), spring barley (Hordeum vulgare), and alfalfa (Medicago sativa).

The study plots are situated in two geomorphologically different parts. Plots in the southern part of the study area lie near the Morava River. The soil types are mainly fluvial soils formed from water sediments of the river, and the altitude is 170 m above sea level. This area falls within the groundwater protection zone, where the use of herbicides listed in the regulations is restricted. The plots in the eastern part of the study area are located at an altitude of 220 m above sea level. The most common soil types are cambizemes and regozemes. Both parts belong to the area, which is characterized by an average annual temperature exceeding 10 °C with an annual rainfall of up to 500 mm [48,49,50]. The Morava River flows through the center of the cadastral territory of Zarazice. Furthermore, there is an artificial water canal—the Baťův kanál on the right bank of the Morava—which is used for recreation purposes. The western border of the cadastral territory is formed by the relief arm of the Morava River, which was built in the 1930s to divert flood flows. The entire area between the relief arm and the Baťa canal is delimited as a protection zone of the water source–Bzenec complex. In this complex, underground water is collected from wells and serves as a mass source of drinking water. The investigated plots in the southern part fall into the second degree Protection Zone, in which the requirements and prohibitions based on the Decision on the Determination of Water Resource Protection Zones from 1990 are respected.

No herbicide limitations (full regulation): In the plots, it is permissible to use all registered herbicides that are approved for the given crop, and their application is governed by general regulations for the use of plant protection products. Herbicides applied to maize crops include BALATON (Terbuthylazine) at a rate of 3.0 L/ha and STORY (Florasulam and Mesotrione) at a rate of 0.3 L/ha. Herbicides applied to winter wheat crops consist of GLEAN 75 PX (Chlorsulfuron) at a rate of 0.02 kg/ha and HURICANE (Aminopyralid, Florasulam, and Pyroxsulam) at a rate of 0.2 kg/ha. Herbicides applied to winter rapeseed crops include BUTISAN STAR (Chlormequat and Metazachlor) at a rate of 2.0 L/ha, GARLAND FORTE (Propaquizafop) at a rate of 0.8 L/ha, and GARLAND FORTE (Propaquizafop) at a rate of 0.5 L/ha.

Herbicide limitations (limitation): Within the designated protective zone plots, chemical weed control is restricted. Only herbicides with granted exceptions are allowed to be used on these plots. Herbicides applied to maize crops include EQUIP ULTRA (foramsulfuron) at a rate of 2.0 L/ha and STORY (Florasulam and Mesotrione) at a rate of 0.3 L/ha. Herbicides applied to winter wheat crops consist of HURICANE (Aminopyralid, Florasulam, and Pyroxsulam) at a rate of 0.2 kg/ha. Herbicides applied to winter rapeseed crops include GLEAN 75 PX (Chlorsulfuron) at a rate of 0.02 kg/ha and HURICANE (Aminopyralid, Florasulam, and Pyroxsulam) at a rate of 0.2 kg/ha.

2.2. Method of Vegetation Assessment

Weed assessments were performed in six plots. Three of these are located in the surface water protection zone. The other three plots were located in a zone in which herbicide use was not restricted. Flint maize, winter wheat, and winter rapeseed were grown in the plots. The plots’ characteristics are listed in

Table 1. Characteristics of selected plots.

Water Protection Zone	Crop	Surface Area (ha)	GPS
No herbicide limitations (full regulation)	Maize	7.12	48.9282369 N, 17.3842381 E
	Winter wheat	11.11	48.9334244 N, 17.3749683 E
	Rapeseed	9.08	48.9294775 N, 17.3726725 E
Herbicide limitations (limitation)	Maize	7.07	48.9418253 N, 17.3554419 E
	Winter wheat	15.95	48.9441083 N, 17.3509789 E
	Rapeseed	8.05	48.9502931 N, 17.3555419 E

. Weeds were assessed using a numerical method. Eight sampling areas with a size of 1 m² were demarcated on each monitored plot. Sampling areas were evenly distributed in the plots. After demarcating the sampling area, the weed species were identified and counted. The taxonomic nomenclature of the plants follows Kaplan et al. [51]. The observations were conducted between March and June 2018.

The identified weed species were categorized into groups based on their biological characteristics. The spring weed group includes annual species that germinate at temperatures of 0–8 °C and do not survive the winter. The summer weed group encompasses annual species that germinate at temperatures of 8 °C and higher and do not survive the winter period. The winter weed group includes annual species that survive winter. The perennial weed group comprises species with multiple growing seasons over several years. The weeding crops group encompasses crops that behave like weeds and grow within other crops as a consequence of previous cropping.

The results were processed using multivariate analyses of ecological data. The first analysis performed was the segmental Detrended Correspondence Analysis (DCA), which calculated the length of the gradient (Lengths of Gradient) and was followed by RDA. Statistical significance was tested using the Monte Carlo test with 999 calculated permutations. All multivariate analyses were performed using CANOCO 5.0 [52]. The necessary calculations were performed using Canoco 5.0 computer program.

3. Results

A total of 23 weed taxa were identified in corn stands, 19 were identified in winter wheat stands, and 16 were identified in winter rapeseed stands within the assessment. The average number of weeds is shown in Figure 1. The representations of the individual weed taxa are shown in Figure 2 (for maize stands), Figure 3 (for wheat stands), and Figure 4 (for rapeseed stands).

The results of the RDA, which evaluated the number of individuals of weed taxa in maize, were significant at the significance level of α = 0.023 for all canonical axes. The differences in weed abundance were statistically significant. A graphical illustration of the results of the RDA is shown in Figure 5.

The results of the RDA, which evaluated the number of individuals of weed taxa in wheat stands, were significant at the level of significance of α = 0.063 for all canonical axes. However, the differences in weed abundance were statistically inconclusive. A graphical illustration of the RDA results is shown in Figure 6.

The results of the RDA, which assessed the number of weed taxa in rapeseed stands, were significant at the significance level of α = 0.023 for all canonical axes. The differences in weed abundance were statistically significant. A graphical illustration of the RDA is shown in Figure 7.

Based on the RDA, the identified plant taxa were divided into three groups. The distribution of taxa into groups according to the RDA is shown in

Table 2. Groups of weeds according to their reaction to limitation of herbicide use (RDA).

Occurence in Crop Stand	Groups of Weeds
	Species Preferring Herbicide Limitation	Species without Any Preference, Affected by Other Factors	Species Preferring Full Herbicide Regulation
Flint maize	AbuTheo—Abutilon theophrasti, AnaArve—Anagallis arvensis, DatStra—Datura stramonium, CheStri—Chenopodium strictum, CheSuec—Chenopodium suecicum, MerAnnu—Mercurialis annua, SetViri—Setaria viridis, SolNigr—Solanum nigrum	AmaRetr—Amaranthus retroflexus, CapBurs—Capsella bursa-pastoris, EchCrus—Echinochloa crus-galli, CheAlbu—Chenopodium album, PerLapa—Persicaria lapathifolia, SteMedi—Stellaria media, ThlArve—Thlaspi arvense, TriAest—Triticum aestivum	AmaPowe—Amaranthus powellii, AnaFoem—Anagallis foemina, CirArve—Cirsium arvense, ElyRepe—Elymus repens, ChePedu—Chenopodium album subsp. Pedunculare, RumCris—Rumex crispus, SetPumi—Setaria pumila
Winter wheat	AnaArve—Anagallis arvensis, CirArve—Cirsium arvense, ElyRepe—Elymus repens	CheAlbu—Chenopodium album, SolNigr—Solanum nigrum, VerHede—Veronica hederifolia	ApeSpic—Apera spica-venti, AtrPatu—Atriplex patula, AveFatu—Avena fatua, BroSter—Bromus sterilis, BroTect—Bromus tectorum, CapBurs—Capsella bursa-pastoris, DesSoph—Descurainia Sophia, GalApar—Galium aparine, MatCham—Matricaria chamomilla, PapRhoe—Papaver rhoeas, PlaUlig—Plantago uliginosa, VerPers—Veronica persica, VioArve—Viola arvensis
Winter rapeseed	GerPusi—Geranium pusillum, PapRhoe—Papaver rhoeas, PlaUlig—Plantago uliginosa, SinArve—Sinapis arvensis, VerHede—Veronica hederifolia, VerPers—Veronica persica	CapBurs—Capsella bursa-pastoris, DesSoph—Descurainia Sophia, MatCham—Matricaria chamomilla, SteMedi—Stellaria media, TriAest—Triticum aestivum, TriInod—Tripleurospermum inodorum, VioArve—Viola arvensis	ApeSpic—Apera spica-venti, LamPurp—Lamium purpureum, ThlArve—Thlaspi arvense

.

The results presented in Figure 1 demonstrate significant differences among the weed groups within the monitored crops. However, the representation of weed groups under the conditions of varied herbicide regulation limitations was not as pronounced.

From the results presented in Figure 2 and Figure 5, it is evident that the limitation of herbicide usage alters the weed species composition in maize. In maize crops, the use of only specific herbicides (limitation) creates more favorable conditions for weed species, such as Setaria viridis, Mercurialis annua, Chenopodium strictum, Solanum nigrum, Abutilon theophrasti, Datura stramonium, and Chenopodium suecicum. Under full regulation conditions, weed species such as Chenopodium album, Setaria pumila, and Elymus repens find it easier to establish themselves.

From the results depicted in Figure 3 and Figure 6, it is evident that the limitation of herbicide usage also alters the weed species composition in winter wheat. The restricted use of herbicides (limitation) creates more favorable conditions for weed species such as Cirsium arvense and Elymus repens. Under full regulation conditions, weed species such as Apera spica-venti, Atriplex patula, Avena fatua, Descurainia Sophia, Galium aparine, Papaver rhoeas, and Veronica persica find it easier to establish themselves.

From the results presented in Figure 4 and Figure 7, it is evident that the limitation of herbicide usage also alters the weed species composition in winter rapeseed. The restricted use of herbicides (limitation) creates more favorable conditions for weed species such as Geranium pusillum, Papaver rhoeas, Plantago uliginosa, Sinapis arvensis, Veronica hederifolia, and V. persica. Under full regulation conditions, weed species such as Apera spica-venti, Lamium purpureum, and Thlaspi arvense are established more easily.

4. Discussion

The weeding of selected crops under real conditions varies based on chemical regulation limitations, which are given by the rules of the Water Protection Zones. The reactions of weeds are manifested primarily in species composition rather than in the intensity of weeding.

Higher weeding and a higher proportion of the weeds Setaria viridis, Mercurialis annua, Chenopodium strictum, and Solanum nigrum were observed in the maize stands where the use of herbicides was restricted. Species that are considered neophytes or species with an invasive status (Abutilon theophrasti, Datura stramonium, and Chenopodium suecicum) were also found in these stands to a greater extent.

The differences in the representation of weeds in the wheat stands were statistically significant according to the RDA. This might have been caused by the low weeding rate, which was implied by the high efficiency of the herbicides allowed in the water protection zones. Nevertheless, perennial weeds (Cirsium arvense and Elymus repens), which are difficult to control and very harmful in wheat stands, were more common in plots with herbicide limitations. The occurrence of perennial weed species is mainly associated with land. Although they spread slowly, there is a risk of spreading from a long-term perspective.

The winter rapeseed stands differed in terms of weed species composition. Geranium pusillum, Papaver rhoeas, Plantago uliginosa, Sinapis arvensis, Veronica hederifolia, and V. persica occurred more frequently in plots with herbicide limitation. These weeds are sensitive to common herbicides but are less sensitive to herbicides permitted in areas with herbicide limitations.

Changes in the species composition of weeds evoked by the limitation of herbicide applications lead to the promotion of more specialized weeds (specialists) and to the exclusion of generally widespread species (generalists). According to Clavel et al. [53], pesticides, especially herbicides, can contribute to the process of “biotic homogenization,” which is the representation of weeds that are resistant to herbicide increase. The heterogeneity of habitats in the landscape is increasing by introducing limitations on the application of herbicides. The reduction in pesticide doses is a fundamental contributor to taxonomic and/or functional diversity in the broader agricultural landscape, according to Chiron et al. [25].

Herbicides co-create a selection pressure on field vegetation [54,55]. Different regulation creates a specific pressure on weed vegetation, to which the plants also respond in the longer term by changing their life strategy [56]. Weeds that can survive this pressure occupy this niche and remain part of the agricultural landscape. Field vegetation under herbicide regulation is important for the abundance of birds [27,57] and other animals that are capable of settling in intensively managed fields [58].

Limiting the use of pesticides in sensitive areas (near water bodies) appears to be justified from the perspective of water protection and biodiversity [59]. The ecosystem response of agricultural land to environmental changes remains understudied [60,61]. Biodiversity and soil fertility are crucial for humanity [62]; therefore, they must be given proper attention. The massive use of pesticides around the world leads to the stabilization and increase in crop yields, but also raises strong concerns about the impacts on biodiversity [63,64,65]. A recent review summarized the results of 394 studies and found that a large number of studies reported significant negative effects of pesticides on soil invertebrates [66,67], which constitutes a significant part of global biodiversity [60,68,69]. They are also an essential part of terrestrial food webs and play an important role in ecosystem services for many terrestrial animals, including vertebrates [70,71,72,73,74]. A loss of biodiversity destabilizes farmland ecosystems, which potentially threatens the sustainable intensification of agriculture [75].

A floristic analysis of the site is a well-known way of assessing the quality of the environment, because the entire flora of the site is a bioindicator [76]. According to Van Kleunen et al. [77], the presence of non-native taxa is an indicator of poor environmental quality. It can be assumed that a simple limitation of herbicide use is not a guarantee of improving the environment or water quality. Several studies have addressed the impacts of government measures and implemented management (for example, ES 2018 and EC 2019) on water quality [78], but little empirical research has been conducted to contribute to improving the quality of underground and surface water [79].

The limitations of chemical weed control resulting from regulations on water protection creates a need for non-chemical weed control in field crop stands. According to Melander et al. [80], research on direct non-chemical methods of weed control uses policy initiatives that aim to reduce the reliance on pesticides and promote organic crop production. The need for non-chemical methods of weed regulation can also be attributed to the lack of new active substances of chemical herbicides, which results from stricter requirements for the registration of pesticides and environmental regulations. This situation caused a drastic decrease in available pesticides, with the loss being the greatest in Europe, with 945 active substances in 1999 compared to 336 in 2009, which resulted in a 64% reduction [81]. Our results show that on plots with herbicide limitations in real conditions, there is an increase in difficult-to-control weeds (Cirsium arvense, Elymus repens, Geranium pusillum, and Setaria viridis) or new species of weeds (Abutilon theophrasti, Mercurialis annua, and Solanum nigrum). Their occurrence requires changes in weed regulation by farmers, which are often reluctantly accepted.

Regulations aimed at water protection are of paramount importance to safeguard the environment and human health. The impact on other ecosystem components must be monitored and evaluated. Limiting the use of herbicides reduces surface water pollution but simultaneously introduces challenges for farmers. Protective and regulatory measures must be understood on a broader scale of the entire landscape. These measures should be assessed not only from the perspective of water protection, but also by considering other landscape components influenced by these regulations. In formulating protective and regulatory measures, multidisciplinary discourse is necessary along with efforts to find collaborative solutions. To ensure the viability and effectiveness of these measures, it is crucial to avoid a scenario in which safeguarding one landscape element (water) significantly disadvantages the other (agriculture).

Therefore, it is essential to look for other techniques and methods to protect surface water. In the entire landscape, buffer zones are very important, and according to Mykrä et al. [82], they are very effective in protecting aquatic environments because of the diversity of plant communities in floodplain forests. Buffer zones or coastal zones are commonly considered to be effective filters of nutrients (N, P), as well as pesticides [83,84,85,86]. However, the relative effectiveness of these buffer zones depends on topography, vegetation and soil type, climate, and the extent of nutrient loading, and probably chiefly on their width [87,88,89,90].

Riparian vegetation affects stream water quality and biodiversity in several ways [87,91,92]. The vegetated riparian zone is important for the degradation of organic agrochemicals, including pesticides [93]. An appropriate design of the buffer zone based on site characteristics and landscape restrictions offers experts a tool to take steps to limit the negative effects of agriculture [94,95].

The need to feed billions of people necessitate reliable and predictable crop yields, with a parallel requirement to preserve conditions for biodiversity. This can be achieved using a model of agricultural production that includes water bodies and respects the multi-function use of productive landscapes [75].

5. Conclusions

Restrictions on weed management within water protection zones, as applied in the Czech Republic, led to alterations in the weed spectrum of the chosen crops. The reaction of field weeds can be seen primarily in the weed species composition. Changes in the vegetation composition were more evident in the stands of maize and winter rapeseed. In winter wheat stands, the differences in the weed composition were not statistically significant. Places with limited herbicide application are mainly suitable for weeds that are less sensitive to permitted herbicides, perennial species, and neophytes. The proportion of neophytes and invasive species was higher, especially in maize stands in plots with herbicide limitation. The responses of weeds to the reduction in pesticide use can help in planning appropriate weed control measures for individual crops.

Water protection rules can cause problems for the regulation of certain weed species. The limited assortment of herbicides leads to the repeated application of herbicides with the same active substance, which can result in the emergence of resistance in weeds. In areas designated for water protection, a complete ban on the use of pesticides appears to be more convenient, and in agricultural production areas, there is a transition to the organic farming regime.

The planning and implementation of appropriate measures for weed control in individual crops should consider specific conditions of a given location and the consequences of the chosen practices. A comprehensive approach to this issue should be based on scientific knowledge, monitoring of the development of weed resistence, and the ongoing optimization of strategies to control them. By adhering to this approach, sustainable agriculture that is in harmony with environmental protection and long-term sustainability can be achieved.

Alternative biological and physical weed control methods could represent a promising direction for further research. A thorough analysis of the economic and environmental aspects of these methods would help in finding a balanced and sustainable solution that would minimize negative impacts on the environment and agricultural production. Educating farmers about optimal weed control practices is also key to achieving sustainable agriculture and the long-term sustainable use of land and water resources.